World War II, also known as the second world war, took place between 1939 and 1945. The war involved nearly every part of the world, with many countries being with the axis powers or the allies. The primary axis powers being Germany, Italy, and Japan and the primary allies being France, Great Britain, the United States, the Soviet Union, and to an extent China. This war resulted in 45,000,000 to 60,000,000 deaths. It's considered one of the bloodiest and longest wars in history.

By 1939 Adolf Hitler, Germany's dictator, was determined to invade Poland violating the Treaty of Versailles. Hitler and Stalin, leader of the Soviet Union, signed the German-Soviet nonaggression pact which worried London and Paris. On September 1st, 1939 Hitler invaded Poland. Great Britain and France guaranteed Poland military support if it ever was invaded so they declared war on Germany. This was the beginning of WWII. 

Adolf Hitler                                         Josef Stalin

On September 17th Soviet troops invaded Poland, which fell by 1940. Germany and the Soviet Union divided control over the nation. On April 9th, 1940 Germany invaded Norway and Denmark and on May 10th swept through Belgium and the Netherlands. On June 14th German forces entered Paris taking half of France.

Hitler had plans of creating a 'master race'. He wanted a 'pure' German race. He believed the war would grant him territory for the German race to expand. One part of this plan was known as the 'final solution' which was a mass extermination of Jewish people throughout German occupied Europe. Over the course of the next three years 4 million Jews lost their lives in concentration camps. 

The other half of this plan was to betray the Soviet Union as they had a lot of territory which would give Hitler his living space. On June 22, 1941 Hitler ordered the invasion of the Soviet Union. This invasion was called operation Barbarossa effectively cutting ties between the two countries and leading the Soviet Union to join the allied forces 

With Britain occupied with Germany in Europe, Japan continued expanding into China. On December 7, 1941 Japan attacked Pearl Harbor, a major US naval base in Hawaii, killing over 2,300 troops. This was a major catalyst for the United States involvement in WWII. The event swayed many U.S. citizens opinion in favor of joining the war. On December 8 congress declared war on Japan  with only one opposing vote. This lead to the axis powers to declare war on the US.