Hitler's dangerous beliefs became reality when he became chancellor. Once in power he instilled laws that oppressed people he thought were undesirables and began building up Germany's military in defiance of the treaty of Versailles. His rise to power would be one of the most important events as this would be the starting point of the eventual outbreak of World War 2, one of the most bloodiest wars in history.
Japan Attacks Pearl Harbor (1941)
After many attempts of the Western Allies' sue for peace with the policy of appeasement, Hitler's invasion of Poland proved to the Allies that appeasement has failed and the only way to stop him is to declare war. This invasion kicked started World War 2 in Europe and is an important event.
Two years after the signing of the non-aggression pact with the Soviet Union and the failure of operation sea lion, Hitler looked toward The Soviet Union as a target for an invasion. This would be known as Operation Barbarossa and would become the bloodiest invasion of the war. This event is important because it is when Stalin joined the Allies and arguably one of the main reasons why the Nazis lost World War 2.
The bombings of Hiroshima and Nagasaki (1945)
Up until 1941 the U.S. remained neutral during the World War 2. The oil embargo imposed on Japan slowed down their military operations and damaged relations between the two nations. In retaliation the Japanese attacked the Hawaiian port of Pearl Harbor in late 1941. Two days after the attack President Roosevelt asked Congress to declare war. This event is important because the attack brought the U.S. into World War Two and marked the beginning of the end of Japanese domination in Asia.
The June 6th invasion of Normandy finally brought Allied troops into western Europe and into France. This would lead into the liberation of France and the occupation of West Germany. This event is important because it began the end of Nazi occupation in Western Europe and prevented as possible soviet invasion of Western Europe and the spread of communism.
By late 1945 The Empire of Japan still refused to surrender after losing much of their conquered lands and been pushed back to their homeland. By this time the U.S. had developed the Atomic Bomb and decided to use it on Japanese cities instead of invading to force Japan to surrender. After using the bombs in Hiroshima and Nagasaki Japan surrenders. This event is the most important because it had led to the end of World War 2 and showed how devastating and dangerous the Atomic Bomb was and it ushered in the Cold War.