WWII happened because countries, such as, the US and Europe were in a depression. Germany followed Adolf Hitler because they were desperate and wanted to get out of the Depression.
After WWI Germany had to pay back the war damages they owed. They couldn't pay them back which caused Germany to go into a depression. When Germany let Adolf Hitler take control as a dictator he said he would get them out of the Depression and started blaming Jews for their problems. Dictators also rose to power in other countries like Italy.
Adolf Hitler was a the leader of the Nazis and later became the dictator of Germany. Since he was a dictator he had complete control over Germany. He invaded Poland, Britain, France, Belgium, Denmark, Norway, Luxembourg, the Netherlands, and the Soviet Union. He came to power by saying he would get them out of the Depression. The United States stayed neutral during these events until December 8, 1941.
Benito Mussolini was Italy's dictator. He invaded Egypt. He came to power by forming the Fascist Party.
Francisco Franco was the dictator of Spain. He invaded French North Africa. He came to power by moving up from the ranks from the Nazis.
Joseph Stalin was the dictator of the Soviet Union. He invaded Poland. He came to power by moving up the ranks in the Bolshevik party after one of the leaders died.
Hideki Tojo was the dictator of Japan. He invaded Pearl Harbor. He came to power by rising in the military ranks.