The 5 Most Important Events of WWII
Japan Attacks Pearl Harbour
On December 7th, 1941 the Japanese attacked Pearl Harbour. This attack brought the United States of America into WWII as a combat force. In addition, the attack on Pearl Harbour also opened the Pacific Theater. Without the Americans entering the war, the invasion of Normandy might have never happened and the Japanese would not have to deal with the Americans in the Pacific and would have much greater success in China. The Americans were responsible for the D-Day invasion and the Japanese surrender so their entrance into the war is 1st in the top 5.
Battle of Britain
From July 1940 to May 1941 the Luftwaffe attacked British factories, airfields, radio towers, and other military assets. During the Blitz period of Nov 1940, Hitler attacked civilian targets for 57 nights. Although the Luftwaffe were superior in numbers, the British were victorious through the use of their superior radar. If the British had not held of the Luftwaffe, the invasion of Britain could have actually happened because without the RAF, the Luftwaffe could overwhelm the Royal Navy. If Britain had been invaded, Hitler would have had taken all of Western Europe and would not have had to fight on two fronts. The British victory of the Battle of Britain held the western front for the Allies and so it is 2nd in the top 5.
Hitler Breaks The Molotov-Ribbentrop Pact
In June 1941, Hitler gives up invading Britain, and instead invades the Soviet Union, breaking the Molotov-Ribbentrop Pact. This brought the Soviets into World War II and introduces a major Allied force that will eventually have a large impact in capturing Berlin. After holding out the winter, the Soviets eventually manage to push back and force Hitler to fight the British and Americans in the West and the Soviets in the East. Without the Russians the victory would have been much harder if possible at all. The Soviets entering the war brought fighting at both ends and so it is 3rd in the top 5.
Hitler Invades Poland
On September 1st, 1939 Hitler invaded Poland. This invasion is what finally led the Allies to declare war on Hitler on September 3rd. This is also the first time Hitler's Blitzkrieg was used in action and it proved very effective. As far as regular military action is concerned, this is the start of the World War II so it is the 4th of the top 5.
Hitler Re-Militarizes Rhineland
In 1936 Hitler Re-Militarized the then De-Militarized Rhineland. This was in direct violation of the Treaty of Versailles and the first hostile act by Hitler. However, the League of Nations did nothing to stop Hitler and this turned out to be only the first of many acts of hostility by Hitler. Hitler's Re-Militarization of Rhineland is the starting point of World War II and so it is 5th in the top 5.