|Cartoon depicting the Neutrality Acts and a cause of WWII.|
As in World War One, the United States did not officially join the war until later. Similarly as before, the United States did not contribute very much to the actual start of the war. Despite this, the United States did not refrain from aiding the Allies after the start of the war, and these actions led by President Roosevelt invariably drew the United States into the War.
Before the war, it was clear that certain countries were showing signs of aggression. Germany was acquiring land through the annexation of Austria and Czechoslovakia in direct violation of the Treaty of Versailles; Italy was beginning to attack Ethiopia and Albania along with siding with Germany; Japan had begun capturing Manchuria and attacking parts of Eastern China. Despite all of this, the United States made no formal actions due to the Neutrality Acts.
The fact that the United States did nothing would have simply allowed Hitler to continue gathering land until the breaking point occurred in Poland. Just as Britain and France did littler to prevent the inevitable, out of fear, out of the US policies the war was brought about. World War Two was caused mainly by the lack of an act of resistance which allowed Germany to simply muster up strength until it was ready to take on the whole Ally Alliance.
Eventually, events began pushing the United States closer into the war. Firstly, the Spanish Civil War had ended by the start of the second World War. In this, the United States would have supported the Republicans if the Neutrality Acts didn't forbid it. Of course, Germany and Italy each supported the Nationalists which would make Spain into a dictatorship under Francisco Franco. Due to the conflict in interest, the United States would begin to resent the two Axis Powers.
Over time, after the war had started, Germany began winning the war with the fall of France and weakness of Britain. Furthermore, things weren't looking good for China either. As the events began unfolding, Roosevelt became anxious to become involved in some way. He therefore issued the Quarantine Speech which called to economically isolate the world dictatorships. However, as this plan received negative public opinion, he retracted the idea.
When Britain began losing money to buy weapons with, Roosevelt decided it was time to help. He issued the Lend Lease Act and Atlantic Charter. The Lend Lease Act would allow Britain to borrow weapons so as long as they are returned. The Atlantic Charted allowed the US to escort merchant ships further into the Atlantic even as far as Iceland so the British navy could remain more concentrated. These events increased the American alliance with Britain and tension with Germany. At the same time, The US had frozen Japanese assets which meant Japan could no longer purchase oil from the US. Without oil, Japan was doomed, and they were looking for desperate measures.
|Bombing of Pearl Harbor|
In 1941, Germany had invaded Russia thus making Russia join the Allies in the war. With this, the United States aided the Soviet Union even though it was communistic and had been for a time the friend of the enemy.
With the US so involved in the war, and Japan becoming embarrassed that without oil, they couldn't progress through the conquerization of China, Japan then bombed Pearl Harbor on December 7, 1941. This single event caused the United States to unanimously declare war on Japan which officially brought it into the war.