The War To End All Wars? Ha. Nice Try.

After World War I, the entire world was walking around with glazed-over eyes, minds collectively boggled by just how nasty things got on the battlefield. The war had ushered in all kinds of scary new technology, from machine guns and aerial warfare to the use of chemicals and poisonous gas.

Want to read a harrowing but brilliant book that explores the horrors of WWI? Check out All Quiet on the Western Front. You'll come away emotionally scarred, but you'll have a pretty good idea why people wanted to nix the whole war thing for good.

American citizens were less than eager to jump head first into another conflict all the way across the world. Lots of people had died, far from their home continent, and lots more were still trying to deal with all the things they'd experienced.

Meanwhile, folks in Germany weren't super happy, either. After they'd surrendered, the Allies blamed them for everything. The Germans had to take responsibility for causing the war—and had to pay everyone back.

It became a perfect storm of unfortunate events—and not the kind with Count Olaf. Germany had to pay reparations, or money to make up for the damages caused by the war, just as the economy around the world started to go up and down like a crazy amusement park ride.

The Great Depression caused problems for everyone, but Germany was perhaps the hardest hit. It got a point where you'd need thousands of reichsmarks to get the equivalent of $1 USD. That's completely insane, and also totally unsustainable. Tension flew through the roof in Germany—everyone was suffering, and there didn't seem to be any real solution.

But then along came a mustachioed man with a big voice and a bigger genocidal tendency.

How To Stop Hitler? By Giving The Allies Some Guns.

Hitler was a powerful speaker who appealed to the hungry and the poor and the unemployed by promising them a better life. When he was appointed chancellor of Germany in 1933, the German people thought everything would get better, that they'd finally move beyond the terrible humiliation of not only losing the war, but taking full responsibility for it.

In efforts to do just that, Hitler started ignoring parts of the Treaty of Versailles, which had ended World War I (and plunked down a huge wartime bill for Germany to pay). Most notably, he started rebuilding the German military, and wasn't at all shy about his plans to make the country the largest superpower in the world.

However, after a while, it became apparent he couldn't do it all by himself, especially with Great Britain and the U.S. not at all excited about his plans for world domination. At the time the Tripartite Agreement was signed in September 1940 (see the Timeline section of the guide for more information), Great Britain was already involved in the war. But the last thing Hitler needed was the U.S. getting any crazy ideas about joining the party. So, along with Italy and Japan, Germany signed a document threatening military action against America if the country tried to interfere.

After that, the Axis were really ready to play—and they had no plans to play fair.

Throughout the rest of 1940, many smaller countries joined the bad guys. And by joined, we mean they were invaded and didn't have much choice. The rest of the world watched it happen, and FDR knew the U.S. needed to act. When he gave his "Great Arsenal of Democracy" speech at the end of the year, three months after the Axis signed the Tripartite Agreement, he made it clear there wasn't any time to waste.

And he was right—less than six months later, in June 1941, the Axis had invaded Greece and put a stop to all resistance efforts.

Within three months, the U.S. was hard at work in plants and factories around the country, manufacturing weapons and machinery for the Allies. In March 1941, FDR officially gave up on that neutrality business and singed the Lend-Lease Act. It gave him the authority to send munitions, money, or any other materials to the Allies in order to stop the Axis from taking over Europe.

And while the president sent lots of goodies to the other side of the Atlantic Ocean, he was doing the exact opposite in the Pacific Ocean. The U.S. wasn't crazy about Japan invading China in 1937, and in response, American officials stopped trading with the Japanese. The idea was that without access to money, oil, and other resources, Japan would have to slow their roll and back off China. That didn't happen, and both the U.S. government and the Japanese government negotiated for quite a long time to try and find a middle ground.

But we know now that didn't happen. The Japanese were done with the official business, and attacked the U.S. at Pearl Harbor on December 7th, 1941. Soon after, they started taking over American islands in the Pacific Ocean, and the United States had no choice but to join the fighting.