World War 2 was caused by factors like the Treaty of Versailles, Japanese expansionism, and Hitler's rise to power in Germany. Key events of the war included Germany invading Poland and attacking Great Britain and the Soviet Union, and Japan attacking Pearl Harbor which led to the US entering the war. Major turning points were the battles of Stalingrad and Normandy, and the war ended with the fall of Berlin and the US dropping atomic bombs on Japan. The war had lasting economic effects in Europe and led to the formation of the United Nations.