During World War II, the United States, Great Britain and the Soviet Union were the main powers that fought on the Allied side against the Axis powers of Germany, Japan and Italy. Other countries that joined forces with the Allied side were France, Australia, Canada, New Zealand, India and Canada.
The Axis powers started World War II when Germany began to invade and occupy smaller European countries, such as Austria and Poland. While Germany was going after most of Europe, Japan wanted to dominate Asia and the Pacific regions of the world. Japan's attack on Pearl Harbor, Hawaii prompted the United States to join the fighting on the Allied side.
While most of the world was pulled into the conflict in one way or another, there were also several countries that managed to stay neutral. Ireland, Portugal, Spain, Sweden and Switzerland all avoided conflict during World War II.
Because so many countries and regions were involved in the war, World War II is considered a global war. Many countries, including Sweden, Switzerland, Ireland and Spain, remained neutral during the war and barely got involved. Though many complex conflicts and incidents built up in the years prior to the war, World War II took place between 1939 and 1945.
On Sept. 1, 1939, Nazi Germany, led by Adolf Hitler, invaded Poland with the intention to continue to take control of Europe. This caused Britain and France to declare war on Germany. Across the world, Japan was also seeking to control most of the Asian continent and the Pacific region. In 1937, Japan battled China in what is now known as the Marco Polo Bridge Incident.
As the conflict spread, more and more countries began to join the war. By the summer of 1940, Germany had seized France, Belgium, Norway, Holland and Denmark. In 1941 Germany attacked the Soviet Union, which initiated that country's involvement. That same year, the Japanese attacked Pearl Harbor in Hawaii, which caused the United States to join forces with the other Allied countries.
The war ended in Europe when Germany's arms decreased and huge numbers of Allied tanks swept back across the continent and took control away from Germany. In 1945, the United States dropped atomic bombs in Japan to end the war in the Pacific. Over the war, approximately 60 million people died.
After several years of fighting, the Allied side was victorious and the war ended in 1945. In one of the last acts of the war, the Allies dropped atomic bombs on the cities of Hiroshima and Nagasaki in Japan. The vast damage led to Japan's surrender and the official end of World War II.