Without any warning, Germany invaded Poland in 1939.

World War II began on Sept. 1, 1939. The war began when Germany invaded Poland. Within days, other countries had joined in on one of the largest conflicts in history. The countries that opposed each other were known as the Axis and Allied powers. The Axis powers consisted of Germany, Italy, Japan, Hungary, Romania and Bulgaria. The Allied powers were the United States, Britain, France, USSR, Australia, Brazil, China, Belgium, Canada, Yugoslavia, South Africa, Poland, Norway, New Zealand, Denmark, Greece and the Netherlands.

Germany Sank U.S. Merchant Ships

One reason that the U.S. joined World War II was that Germany began to attack U.S. supply ships. The United States was neutral at the beginning of World War II. The United Kingdom, being a small island nation, was very dependent on imported goods. The U.S. sent guns, bombs, jeeps, tanks, fuel and more supplies that the United Kingdom would need for the war. The fact that the U.S. sent military aid to the United Kingdom was viewed by Germany as a hostile act.

Japan's Invasions on China

A second reason the United States entered World War II was because of Japan's attacks on China. Japan became aggressive toward China in 1937, a few years before the start of World War II. By 1941, Japan occupied much of north and coastal China. Japan continued its attacks against China. The Japanese committed brutal atrocities against the Chinese. The United States did not like Japan's continuous attempts to overtake Chinese cities. They also did not like the cruel treatment against the Chinese people.

Japanese Attack on Pearl Harbor

On Dec. 7, 1941, the Japanese launched a surprise attack on the U.S. navy base in Hawaii. The Japanese thought that if they attacked Pearl Harbor, the United States would be unable to build ships fast enough to continue to help other Allied countries. This was not the case, however. The U.S. went to war with Japan on Dec. 8, 1941. On Dec. 11, Germany and Italy declared war on the United States.

The End of WW2

The Allied Powers made numerous attempts to end the war; however, Japan had no regard for the lives of its soldiers or its citizens. They were determined to build a fortress around Japan and continue fighting. Hundreds of thousands of lives would have been lost. U.S. President Harry S.Truman made the decision to use nuclear weapons against Japan. On Aug. 6, 1945, the U.S. dropped a nuclear bomb was on Hiroshima, Japan. On Aug. 9, 1945, another nuclear bomb was detonated over Nagaski, Japan. On Aug. 15, 1945, Japan surrendered.