1. Allied Countries
1.1. United States
1.1.1. Although the war began with Nazi Germany's attack on Poland in September 1939, the United States did not enter the war until after the Japanese bombed the American fleet in Pearl Harbor, Hawaii, on December 7, 1941.
1.2. Great Britain
1.2.1. Germany invaded Poland on September 1, 1939. Since Great Britain had pledged military support to Poland if it were attacked by the Germans, it subsequently declared war against Germany on September 3, 1939, hence beginning World War II.
1.3. France
1.3.1. From 1939 to 1940, there was very little fighting. Then the Germans invaded and defeated France and forced the British off the continent mainland. France formally surrendered to Germany and was under their control for 4 years.
1.4. Soviet Union
1.4.1. On August 23, 1939, Germany and the USSR signed a secret non-agression pact dividing up Poland. In September, the Soviets invaded eastern Poland.
1.4.1.1. But Stalin could not avoid war with the Axis powers. On June 22, 1941, Germany invaded Russia, thereby beginning Operation Barbarossa and now Germany was fighting a 2-front war.
2. Axis Countires
2.1. Nazi Germany
2.1.1. After World War One ended in 1918, Germany had to give up land and was banned from having armed forces. In 1933 Adolf Hitler, who led a political party in Germany called the National Socialists or Nazis. He promised to make his country great again and quickly began to arm Germany again and to seize land from other countries.
2.2. Empire of Japan
2.2.1. Japan had begun a period of imperialistic expansion some years before. They had invaded China, the Philippines, and several other countries and seemed hell-bent on taking over all of Southeast Asia. The activity worried the United States. As a result, the United States placed an oil embargo against Japan to slow their expansion. Japan took this as an act of war and then made plans for at attack on the American Fleet.
2.3. Fascist Italy
2.3.1. On November 1, 1936, Germany and Italy, reflecting their common interest in destabilizing the European order, announced a Rome-Berlin Axis one week after signing a treaty of friendship.