When, Why, and How did the United States enter WW2? The Date America Joins the Party

| , | January 24, 2024

It’s September 3rd, 1939. The late summer sun is making one of its final descents, but the air remains heavy and warm. You’re sitting at the kitchen table, reading the Sunday Times. Your wife, Caroline, is in the kitchen, preparing the Sunday meal. Your three sons are on the street below, playing.

There was a time, not so long ago, when Sunday dinners were a source of great joy. Back in the 20s, before the crash and when your parents were alive, the whole family gathered each week to break bread. 

It was normal to have fifteen people in the apartment, and for at least five of those people to be kids. The chaos was overwhelming, but when everyone left, the silence reminded you of the abundance in your life.

But now those days are just distant memories. Everyone — everything — is gone. Those who remain hide from one another so as to not share their desperation. It has been years since you invited anyone over for Sunday dinner.

Breaking away from your thoughts, you look down at your paper and see the headline about the war in Europe. The image below is of German troops marching through Warsaw. The story tells what’s happening, and how people in the United States are reacting.

Staring at the photo, you realize the Poles in the background are blurry, their faces mostly obscured and hidden. But still, despite the lack of detail, you can sense a sadness, a defeatedness, in their eyes. It fills you with unease.

From the kitchen, a crescendo of white-noise roars and pulls your eyes up. Caroline has turned the radio on, and she is tuning rapidly. Within seconds, the voice of President Franklin D. Roosevelt blankets the air. He says,

“It is easy for you and for me to shrug our shoulders and to say that conflicts taking place thousands of miles from the continental United States, and, indeed, thousands of miles from the whole American Hemisphere, do not seriously affect the Americas — and that all the United States has to do is to ignore them and go about (our) its own business. Passionately though we may desire detachment, we are forced to realize that every word that comes through the air, every ship that sails the sea, every battle that is fought does affect the American future.”

FDR Library

You smile at his ability to capture the minds of America; his ability to use understanding and compassion to quiet people’s nerves while coaxing them into action. 

You’ve heard Hitler’s name before, many times. He is a fearmonger and has his sights on war. 

He absolutely needs to be stopped, but he is far away from American soil. The countries closest to him, the ones he actually threatened, such as France and Great Britain — Hitler is their problem. 

How could he possibly affect me? you think, protected by the buffer of the Atlantic Ocean.

Finding consistent work. Paying the bills. Feeding your wife and three sons. That’s your priority in these hard times. 

The war in Europe? That’s not your problem.

Short-Lived Neutrality

For most Americans living in 1939 and 1940 America, the war in Europe was troubling, but the real danger lurked in the Pacific as the Japanese sought to exert their influence in waters and lands claimed by the United States.

Yet, in 1939, with the war in full swing all across the globe, the United States remained officially neutral, as it had done for most of its history and as it had tried but failed to do during World War I.

The Depression was still raging in many parts of the country, meaning poverty and hunger for large chunks of the population. A costly, and deadly, overseas war was not a priority. 

That would soon change, and so would the course of the entire nation’s history.

When did the US enter World War 2

The United States officially entered World War 2 on December 11, 1941. Mobilization began when the United States declared war on Japan on December 8, 1941, one day after the attacks on Pearl Harbor. Because the attack happened without a declaration of war and without explicit warning, the attack on Pearl Harbor was later judged in the Tokyo Trials to be a war crime.

The US’ declaration of war caused Nazi Germany, an ally of Japan at the time, to declare war on the United States on December 11th, sucking the United States into the European Theater of this global conflict, and taking the United States, in just four short days, from a peacetime nation to one that was preparing for all-out war with two enemies on opposite sides of the globe.

Unofficial Participation in the War: Lend-Lease

Although formal declarations of war did not come until 1941, one could argue that the United States had been involved in World War II for some time already, since 1939, despite the country’s self-proclaimed neutrality. It had played a role by supplying Germany’s opponents — which, by 1940, after the Fall of France to Hitler and Nazi Germany, included pretty much only Great Britain — with supplies for the war effort. 

The assistance was made possible by a program known as “Lend-Lease” — legislation that gave the president, Franklin D. Roosevelt, exceptional authority when negotiating deals with nations at war with Nazi Germany and its allies. In December 1940 Roosevelt accused Hitler of planning world conquest and ruled out any negotiations as useless, calling for the United States to become an “arsenal of democracy” and promoting Lend-Lease programmes of aid to support the British war effort.

Essentially, it allowed President Franklin D.Roosevelt to “lend” whatever equipment he wanted (as if borrowing stuff that was likely to get blown up was even possible) at a price Roosevelt determined to be most fair. 

This power made it possible for the United States to give large quantities of military supplies to Great Britain at very reasonable terms. In most cases, there was no interest and repayment didn’t need to happen until five years after the war, a deal that allowed Great Britain to request the supplies it needed but that it could never hope to afford. 

President Roosevelt saw the benefit of this program not only as a way to help a powerful ally but also as a way to jumpstart the struggling economy in the United States, which had been suffering from the Great Depression brought on by the 1929 Stock Market Crash. So, he asked Congress to fund the production of military equipment for Lend-Lease, and they responded with $1 billion, which was later bumped to almost $13 billion. 

Over the next few years, Congress would extend Lend-Lease to even more countries. It’s estimated that the United States sent more than $35 billion in military equipment to other nations around the world so that they could continue to wage effective war against Japan and Nazi Germany.

This shows that the United States was far from neutral, no matter its official status. President Roosevelt and his advisors likely knew the United States would end up going to war, but it would take some time and a drastic shift in the public’s opinion to do so. 

This “drastic shift” wouldn’t happen until December of 1941, with the violent loss of thousands of unsuspecting American lives.

Why Did the United States Enter WWII?

Answering this question can be complicated if you want it to be. World War II was a catastrophic clash of global power, driven primarily by a small group of powerful elites, but played out on the ground by regular working-class people whose motivations were as diverse as they were.

A great many were forced, some signed up, and a number of them fought for reasons we may never understand. 

In total, 1.9 billion people served in World War II, and around 16 million of them were from the United States . Every American was motivated differently, but the vast majority, if asked, would have named one of a few reasons for why they supported the war and even chose to risk their life to fight in it.

Provocation from the Japanese

Larger historical forces eventually brought the United States to the brink of World War II, but the direct and immediate cause that led it to officially entering the war was the Japanese attack on Pearl Harbor. 

This blindside assault came in the early morning of December 7, 1941 when 353 Japanese Imperial bombers flew over the Hawaiin naval base and dumped their payloads full of destruction and death. They killed 2,400 Americans, wounding 1,200 more; sunk four battleships, damaged two others, and wrecked countless other ships and planes stationed at the base. The vast majority of the U.S. sailors killed at Pearl Harbor were junior enlisted personnel. At the time of the attack, nine civilian aircraft were flying in the vicinity of Pearl Harbor. Of these, three were shot down.

There was talk of a third wave of attack on Pearl Harbor as several Japanese junior officers urged Admiral Chūichi Nagumo to carry out a third strike in order to destroy as much of Pearl Harbor’s fuel and torpedo storage, maintenance, and dry dock facilities as possible. Nagumo, however, decided to withdraw as he did not have enough resources to pull off a third wave of attack.

The tragedy of the Pearl Harbor attack, along with its treacherous nature, infuriated the American public — which had been growing increasingly skeptical of Japan due to its expansion in the Pacific throughout 1941.

As a result, after the attacks, America was nearly in complete agreement about seeking vengeance through war. A Gallup poll taken days after the formal declaration found that 97% of Americans were in support of it. 

In Congress, the feeling was equally as strong. Just one person from both houses, a woman named Jeanette Rankin, voted against it. 

Interestingly, Rankin — the nation’s first female congresswoman — had also voted against the United States entering World War I, and had been voted out of office for taking the position. Once back in Washington, she was the sole dissenter in an even more popular vote on war, claiming President Roosevelt wanted the conflict to promote his business interests and also that her pacifist views prevented her from supporting the idea. 

She was ridiculed for this position and accused of being an enemy sympathizer. Newspapers began calling her “Japanette Rankin,” among other things, and this eventually debased her name so thoroughly that she did not run for re-election back into Congress in 1942, a decision that ended her career in politics. 

Rankin’s story proves the nation’s blood-boiling anger towards the Japanese after Pearl Harbor. The carnage and cost that comes with war no longer mattered, and neutrality, which was the preferred approach just two years earlier, ceased to be an option. Throughout the war, Pearl Harbor was frequently used in American propaganda.

The nation had been attacked in its own territory, and someone had to pay. Those who stood in the way were cast aside, and the United States prepared to exact its revenge. 

The Fight Against Fascism

Another reason the United States entered World War II was due to the rise of one of history’s most ruthless, cruel, and vile leaders: Adolph Hitler. 

Throughout the 1930s, Hitler had risen to power preying on the desperation of the German people — promising them a return to glory and prosperity from the starving, military-less position they’d been forced into after World War I. These promises unceremoniously devolved into fascism, allowing for the formation of one of the most brutal regimes in history: the Nazis. 

However, in the beginning, most Americans weren’t overwhelmingly concerned with this phenomenon, instead distracted by their own plight brought on by the Great Depression. 

But by 1939, when Hitler invaded and annexed Czechoslovakia (after he explicitly said he wouldn’t) and Poland (which he also promised to leave alone) more and more Americans began supporting the idea of war with Nazi Germany.

These two invasions made Hitler’s intentions clear to the rest of the world. He cared solely about conquest and domination, and he was unconcerned about the cost. His actions spoke of his view that human life and basic decency meant nothing. The world would bend to the Third Reich, and those who didn’t would die.  

Clearly, the rise of such an evil across the pond was troubling to most Americans, and ignoring what was happening became a moral impossibility. But with two powerful nations — France and Great Britain — willing to stand up to Nazi Germany, and an ocean separating the United States from Europe, most Americans felt safe and didn’t think they would need to step in and help stop Hitler. 

Then, in 1940, France fell to the Nazis in a matter of weeks. The political collapse of such a powerful nation in such a short period of time shook the world and made everyone wake up to the severity of the threat posed by Hitler. At the end of September 1940, the Tripartite Pact formally united Japan, Italy, and Nazi Germany as the Axis Powers.

It also left Great Britain as the sole defender of the “free world.” 

As a result, public support for the war grew throughout 1940 and 1941. Specifically, in January of 1940, just 12% of Americans supported the war in Europe, but by April of 1941, 68% of Americans agreed with it, if it was the only way to stop Hitler and the Axis powers (which included Italy and Japan — both with power hungry dictators of their own).

Those in favor of entering the war, known as “interventionists,” claimed that allowing Nazi Germany to dominate and destroy the democracies of Europe would leave the United States vulnerable, exposed, and isolated in a world controlled by a brutal fascist dictator. 

In other words, the United States had to get involved before it was too late.

This idea that the United States was going to war in Europe to stop Hitler and fascism from spreading and threatening the American way of life was a powerful motivator and helped make the war a popular thing in the early 1940s. 

In addition, it pushed millions of Americans to volunteer for service. A deeply nationalist nation, United States society treated those who served as patriotic and honorable, and those who were fighting felt they were standing up to the evil spreading in Europe in defense of the democratic ideals that America embodied. And it wasn’t just a small group of fanatics who felt this way. In total, just under 40% of the soldiers who served in World War II, which works out to about 6 million people, were volunteers. 

The rest were drafted — the “Selective Service” was established in 1940 — but no matter how people wound up in the military, their actions are a huge part of the story of America in World War II.

The United States Military in World War II

While World War II had its roots in the corrupt political ambitions of dictators, it was fought by regular people from all over the world. In the United States alone, a little more than 16 million people served in the military, with 11 million serving in the army.

The US population at the time was just 150 million, meaning over 10% of the population was in the military at some point during the war. 

These numbers are even more dramatic when we consider that the American military had less than 200,000 soldiers in 1939. The draft, also known as the Selective Service, helped swell the ranks, but volunteers, as previously mentioned, made up a large part of the American military and contributed significantly to their numbers.

The United States required such a massive military as it essentially had to fight two wars — one in Europe against Nazi Germany (and to a lesser extent, Italy) and another in the Pacific against Japan. 

Both enemies had enormous military and industrial capacity, so the US needed to match and exceed this force to even have a chance at winning. 

And because the US was left free from bombings and other attempts to derail industrial production (both Japan and Nazi Germany struggled in the later years of the war to keep their militaries supplied and replenished due to diminishing capacity at home), it was able to build a distinct advantage that ultimately allowed it to be successful.

However, as the US worked to match — in just a few short years — the production efforts Germany and Japan had spent the previous decade developing, there was little delay to the fighting. By 1942, the US was in full engagements with first Japan, and then later Germany.

Early in the war, draftees and volunteers were typically sent to the Pacific, but as the conflict went on and the Allied forces began planning an invasion of Germany, more and more soldiers were sent to Europe. These two theaters were very different from one another and tested the United States and its citizens in different ways. 

Victories were costly, and they came slowly. But a commitment to fighting and an unprecedented military mobilization put the US in a good position for success. 

The European Theater

The US formally entered the European Theater of World War II on December 11, 1941, only days after the events of Pearl Harbor, when Germany declared war on the United States. On Jan. 13, 1942, German U-boat attacks officially started against merchant ships along the Eastern Seaboard of North America. From then until early August, German U-boats dominated the waters off the East Coast, sinking fuel tankers and cargo ships with impunity and often within sight of shore. However, the United States would not begin fighting the German forces until November 1942, with the launch of Operation Torch. 

This was a three-pronged initiative commanded by Dwight Eisenhower (the soon-to-be Supreme Commander of all Allied forces and future President of the United States) and was designed to provide an opening for an invasion of Southern Europe as well as launch a “second front” of the war, something the Russian Soviets had been requesting for some time to make it easier to stop the German advance into their territory — the USSR.

Interestingly, in the European theater, with the fall of France and with Britain’s desperation, the US was forced to ally with the Soviet Union, a nation it greatly mistrusted (and would square off with at the end of the war, well into the modern era). But with Hitler trying to invade the Soviet Union, both sides knew that working together would help each other separately, as it would split the German war machine in two and make it easier to overcome. 

There was much debate as to where the second front should be, but commanders of the Allied forces eventually agreed on North Africa, which was secured by the end of 1942. The Allied forces then set their sights on Europe with the Invasion of Sicily (July–August 1943) and the subsequent invasion of Italy (September 1943).

This put Allied forces on mainland Europe for the first time since France had fallen to Germany back in 1941 and essentially marked the beginning of the end for Nazi Germany. 

It would take two more years and millions more human lives for Hitler and his cronies to accept this truth, giving up in their quest to terrorize the free world into submitting to their heinous, hate-filled, and genocidal regime.

The Invasion of France: D-Day

The next major American-led offensive was the invasion of France, also known as Operation Overlord. It was launched on June 6, 1944 with the Battle of Normandy, known by the code name given to the first day of attack, “D-Day.” 

For Americans, this is probably the most important day of World War II next to (or in front of) Pearl Harbor. 

This is because the fall of France had made the US realize the seriousness of the situation in Europe and dramatically increase the appetite for war. 

As a result, when formal declarations first came in December 1941, the goal was always to invade and regain France before crashing into the German mainland and starving the Nazis of their source of power. This made D-Day the much-anticipated beginning of what many believed would be the final phase of the war.

After securing a costly victory at Normandy, the Allied forces were finally on mainland Europe, and throughout the summer of 1944, Americans — working with large contingents of British and Canadian soldiers — fought their way through France, into Belgium and the Netherlands. 

Nazi Germany decided to make a counteroffensive in the winter of 1944/45, which led to the Battle of the Bulge, one of the more famous battles of World War II due to the difficult conditions and the very real possibility of a German victory that would have extended the war. 

Stopping Hitler, though, allowed Allied forces to move further east into Germany, and when the Soviets entered Berlin in 1945, Hitler committed suicide and the German forces issued their formal, unconditional surrender on May 7th of that year.

In the US, May 7th became known as V-E (Victory in Europe) Day and was celebrated with fanfare in the streets. 

While most American soldiers would soon return home, many remained in Germany as an occupying force while peace terms were negotiated, and many more remained in the Pacific hoping to soon bring the other war — the one still being waged against Japan — to a similar conclusion.

The Pacific Theater

The attack on Pearl Harbor on December 7, 1941 thrust the United States into war with Japan, but most people at the time believed victory would be had quickly and without too heavy a cost. 

This turned out to be a gross miscalculation of both the capabilities of the Japanese military and its zealous commitment to fight. 

Victory, as it happened, would only come after the blood of millions had been spilled into the royal blue waters of the South Pacific.

This first became clear in the months following Pearl Harbor. Japan managed to follow up their surprise attack on the American naval base in Hawaii with several other victories throughout the Pacific, specifically at Guam and the Philippines — both American territories at the time.  

The fight over the Philippines was an embarrassing defeat for the US — some 200,000 Filipinos died or were captured, and around 23,000 Americans were killed — and demonstrated that defeating the Japanese was going to be more challenging and costly than anyone had predicted. 

After losing in the country, General Douglas MaCarthur — the Field Marshall for the Philippine Army and later the Supreme Commander of the Allied forces , Southwest Pacific Area — fled to Australia, abandoning the people of the Philippines. 

To ease their concerns, he spoke directly to them, assuring them, “I shall return,” a promise he would fulfill less than two years later. This speech became a symbol of America’s willingness and commitment to fighting and winning the war, one that it saw as critical to the future of the world.

Midway and Guadalcanal

After the Philippines, the Japanese, as most ambitious imperial countries who have experienced success would do, began trying to expand their influence. They aimed to control more and more of the islands of the South Pacific, and plans even included an invasion of Hawaii itself. 

However, the Japanese were stopped at the Battle of Midway (June 4–7, 1942), which most historians argue was a turning point in the Pacific Theater of World War II. 

Up until this moment, the United States had failed to stop its enemy. But this was not the case at Midway. Here, the United States crippled the Japanese military, particularly their Air Force, by downing hundreds of planes and killing a significant amount of Japan’s most skilled pilots. This set the stage for a series of United States victories that would turn the tide of war in favor of the Americans.

The next major American victory came at the Battle of Guadalcanal, also known as the Guadalcanal Campaign, which was fought over the course of the fall of 1942 and winter of 1943. Then came the New Guinea Campaign, the Solomon Islands Campaign, the Mariana and Palau Islands Campaign, the Battle of Iwo Jima, and later the Battle of Okinawa. These victories allowed the United States to march slowly north towards Japan, reducing its influence and making an invasion possible.

But the nature of these victories made the idea of invading the Japanese mainland a terrifying thought. More than 150,000 Americans had died fighting the Japanese throughout the Pacific, and part of the reason for these high casualty numbers was because almost all battles — which took place on small islands and atolls scattered throughout the South Pacific — were fought using amphibious warfare, meaning soldiers had to charge onto a beach after landing a boat near the shore, a maneuver that left them completely exposed to enemy fire. 

Doing this on the shores of Japan would cost an unfathomable number of American lives. Plus, the tropical climate of the Pacific made life miserable, and soldiers had to deal with a wide range of diseases, such as malaria and dengue fever. 

(It was the perseverance and success of these soldiers in spite of such conditions that helped the Marine Corps gain prominence in the eyes of American military commanders; eventually leading to the creation of the Marines as a distinct branch of the United States Armed Forces.) 

All of these factors meant that in the spring and early summer of 1945, American commanders were seeking an alternative to an invasion that would bring World War II to a hasty close. 

Options included a conditional surrender — something few wanted as this was seen as being too lenient on the Japanese — or the continued firebombing of Japanese cities. 

But advances in technology had given rise to a new type of weapon — one that was far more powerful than anything ever used before in history, and by 1945, American leaders were seriously discussing using it to try and close the book on the war with Japan. 

The Atomic Bombs

One of the most prominent and pressing things that made the war in the Pacific so challenging was the Japanese manner of fighting. Kamikaze pilots defied all ideas of self-preservation by committing suicide via ramming their planes into American ships — causing tremendous damage and leaving American sailors to live in constant fear. 

Even on land, Japanese soldiers refused to surrender, the country’s forces often fighting until the very last man, even when victory was impossible — an approach that inflated the number of casualties experienced by both sides. 

To put it in perspective, more than 2 million Japanese soldiers died in their many campaigns across the Pacific. That’s the equivalent of wiping an entire city the size of Houston, Texas right off the map. 

As a result, American officials knew that to win the war in the Pacific, they had to break the will of the people and their desire to fight. 

And the best way they could think to do this was to bomb Japanese cities to smithereens, killing civilians and (hopefully) pushing them to get their leaders to sue for peace. 

Japanese cities at the time were constructed mainly using wood, and so napalm and other incendiary weapons had a tremendous effect. This approach, which was carried out over the course of nine months in 1944–1945, after the United States had moved far enough North in the Pacific to support bomber raids on the mainland, produced some 800,000 Japanese civilian casualties.

In March of 1945, United States bombers dropped more than 1,600 bombs on Tokyo, lighting the nation’s capital on fire and killing more than 100,000 people in a single night.

Insanely, this massive loss of human life did not seem to phase Japanese leadership, many of whom believed death (not their own, obviously, but those of Japanese subjects) was the ultimate sacrifice to be made for the emperor. 

So, despite this bombing campaign and a weakening military, Japan in mid-1945 showed no signs of surrendering. 

The United States, eager as ever to end the war as quickly as possible, elected to use atomic weapons — bombs possessing never-before-seen destructive potential — on two Japanese cities: Hiroshima and Nagasaki.

READ MORE: Who Invented the Atomic Bomb? The History of the “Destroyer of Worlds”

They killed 200,000 people immediately and tens of thousands more in the years after the bombings — as it turns out nuclear weapons have rather long-lasting effects, and by dropping them, the United States subjected residents of these cities and surrounding areas to death and despair for decades after the war.

American officials justified this staggering loss of civilian life as a way of forcing Japan’s unconditional surrender without having to launch a costly invasion of the island. Considering that the bombings took place on August 6th and August 8th, 1945, and Japan indicated its desire to surrender only days later, on August 15th, 1945, this narrative appears to check out. 

On the outside, the bombs had the intended effect — the Pacific Theater and all of World War II had come to a close. The ends had justified the means.

But underneath this, it’s also equally as likely that American motivation was to establish their post-war dominance by demonstrating their nuclear capacity, especially in front of the Soviet Union (everyone had heard about the bombs, but the US wanted to show they were prepared to use them).

We can suspect something fishy largely because the United States wound up accepting a conditional surrender from Japan that allowed the emperor to retain his title (something the Allies had said was completely off the table before the bombings), and also because the Japanese were likely far more concerned about a Soviet Invasion in Manchuria (a region in China), which was an initiative that began in the days between the two bombings. 

Some historians have even argued that this was what really forced Japan to surrender — not the bombs — meaning this ghastly targeting of innocent human beings had pretty much no impact on the outcome of the war at all. 

Instead, it merely served to make the rest of the world scared of post-World War II America — a reality that still, very much, exists today. 

The Homefront During the War

The reach and scope of World War II meant that practically no one could escape its influence, even safe at home, thousands of miles away from the nearest front. This influence manifested itself in many ways, some good and some bad, and is an important part of understanding the United States during this pivotal moment in world history.

Ending the Great Depression

Perhaps the most significant change that occurred in the United States as a result of World War II was the revitalization of the American economy. 

In 1939, two years before the United States entered the conflict, unemployment was at 25%. But that dropped to just 10% shortly after the US officially declared war and began mobilizing its fighting force. In total, the war generated some 17 million new jobs for the economy. 

In addition, living standards, which had plummeted during the 1930s as the Depression wreaked havoc on the working class and sent many people to the poorhouse and bread lines, began to rise as more and more Americans — working for the first time in many years — could once again afford consumer goods that would have been considered pure luxuries in the thirties (think clothes, decorations, specialty foods, and so on). 

This resurgence helped build up the American economy into one that could continue to thrive even after the war ended. 

In addition, the GI Bill, which made it easier for returning soldiers to buy homes and find jobs, further jump started the economy, meaning that by 1945, when the war was over, the United States was poised for a period of much-needed yet unprecedented economic growth, a phenomenon that further solidified it as the world’s premier superpower in the post-war era.

Women During the War

The massive economic mobilization brought on by the war meant United States factories needed workers for the war effort. But since the American military also needed soldiers, and fighting took precedence over working, factories often struggled to find men to work in them. So, to respond to this labor shortage, women were encouraged to work in jobs previously considered suitable only for men.

This represented a radical shift in the American working class, as women had never before participated in labor at such high levels. Overall, female employment rates jumped from 26% in 1939 to 36% in 1943, and by the end of the war, 90% of all able-bodied single women between the ages of 18 and 34 were working for the war effort in some capacity. 

Factories were producing anything and everything the soldiers needed — clothes and uniforms to firearms, bullets, bombs, tires, knives, nuts, bolts, and so much more. Funded by Congress, American industry set out to create and build everything the nation needed to win.

Despite this progress, once the war concluded, most women who had been hired were let go and their jobs were given back to men. But the role they played would never be forgotten, and this era would propel the movement for gender equality continuing forward.


After the Japanese attacked Pearl Harbor and the Germans declared war, the United States, which had always been a land of immigrants but also one that struggled to deal with its own cultural diversity, started turning inward and wondering if the threat of the enemy was closer than the distant shores of Europe and Asia. 

German, Italian, and Japanese Americans were all treated suspiciously and had their allegiance to the United States questioned, making a difficult immigrant experience all that much more challenging. 

The United States government took things one step further in trying to seek out the enemy within. It started when President Franklin D. Roosevelt issued Presidential Proclamations 2525, 2526, and 2527, which directed United States law enforcement agencies to seek out and detain potentially dangerous “aliens” — those who were not born in the United States or who were not full citizens. 

This eventually led to the formation of large internment camps, which were essentially prison communities where people who were thought to pose a threat to United States national security were held throughout the war or until they were deemed not to be dangerous. 

Most people think only of the Nazi’s murder of Jewish people when they hear the term “camp” in reference to World War II, but the existence of American internment camps disproves this narrative and reminds us how harsh things can get during times of war. 

In total, some 31,000 Japanese, German, and Italian citizens were held in these facilities, and often the only charge against them was their heritage. 

The United States also worked with Latin American countries to deport nationals into the United States for internment. Altogether, because of this policy, more than 6,000 people were sent to the United States and held in internment camps until their case was reviewed and they were either allowed to leave or were forced to stay.

Of course, the conditions in these camps were nowhere near as terrible as the concentration death-camps established by the Nazis across Europe, but this does not mean life in American internment camps was good. There were schools, churches, and other facilities, but communication with the outside world was restricted, and most camps were secured by armed guards — a clear indication that no one was going to leave without permission. 

Xenophobia — a fear of foreigners — has always been an issue in the United States, but the way in which government and regular people treated immigrants during World War II is a topic that has been consistently swept under the rug, and it suggests the narrative of World War II as being Pure Good vs. Pure Evil might not be as ironclad as it’s often presented.

The Impact of the War on Modern America

World War II was fought more than 70 years ago, but it’s impact can still be felt today. Modern organizations such as the United Nations and the World Bank were created in the wake of the war and still have tremendous influence in the 21st century. 

The United States, which emerged as one of the war’s victors, used its success to become a world superpower. Though, immediately after the war, it suffered a brief economic slowdown, this soon turned into a boom unlike any seen before in American history, leading to unprecedented prosperity during the 1950s. 

The Baby Boom, which caused the United States population to swell, contributed to growth and defined the post-war era. Baby Boomers still make up the largest generation in the United States today, and they have a tremendous impact on culture, society, and politics.

The United States also remained heavily involved in Europe, as policies such as the Marshall Plan were designed to help rebuild after the destruction throughout the continent while also advancing United States power in international affairs and containing communism. 

But this rise to dominance was not uncontested. 

The Soviet Union, despite suffering catastrophic losses during the war, also emerged as one of the world’s superpowers and as the biggest threat to global United States hegemony.

The harsh communist dictatorship in the Soviet Union, led at the time by Joseph Stalin, clashed with the United States, and as they sought to expand their sphere of influence to the many newly-independent nations of the post-war era, the United States responded with force to try and stop them and also advance its own interests, hoping to use its military to define a new chapter in world history.

This put the two former allies against one another, and they would fight, although indirectly, war after war in the 1940s, 50s, 60s, 70s, and 80s, with the most well-known conflicts being those fought in Korea, Vietnam, and Afghanistan. 

Combined, these “disagreements” are better known as the Cold War, and they have had a powerful impact in shaping the balance of power in today’s world.

As a result, it seems that even the carnage of World War II — which killed some 80 million people, around 3–4% of the entire world’s population — couldn’t bring humanity’s thirst for power and mystifying obsession with war to an end… and perhaps nothing ever will.


WW2 Timeline and Dates

Adolph Hitler

Erwin Rommel

Anne Frank

Joseph Mengele

Japanese Internment Camps

How to Cite this Article

There are three different ways you can cite this article.

1. To cite this article in an academic-style article or paper, use:

Matthew Jones, "When, Why, and How did the United States enter WW2? The Date America Joins the Party", History Cooperative, February 9, 2020, https://historycooperative.org/when-did-the-us-enter-ww2/. Accessed July 19, 2024

2. To link to this article in the text of an online publication, please use this URL:


3. If your web page requires an HTML link, please insert this code:

<a href="https://historycooperative.org/when-did-the-us-enter-ww2/">When, Why, and How did the United States enter WW2? The Date America Joins the Party</a>

Leave a Comment