Adolf Hitler did not live a long life, but he did live long enough to cause such a great deal of disaster and mistake. WWII went from 1939-1943 and Hitler made many errors but he clearly made three great mistakes. In the Battle of Britain, D-Day and The Invasion of Russia. The war was clearly lost to Hitler's strategic mistakes.
One of Hitler's earliest mistakes was made in august 8, 1940; during the battle of Britain. Germany sent the Luftwaffe on a rampage against British towns and seaports. Hitler wanted London to pay for bombing a few of Germany's towns. One million pounds of bombs were dropped on the city of Coventry in one single raid. (www.battleofbritain.com/bobindex.htm) While Hitler was targeting civilians it gave time for the RAF to rebuild and become more prepared for the Germans. The Luftwaffe lost 700 aircraft's and the Britishlost160. (www.battleofbritain.com/bobindex.htm) Because of the loss Hitler decided to change plans, which meant using more fighters and fewer slow bombers, now the aim was on civilians. It was a mistake made by Hitler to attack the civilians, Hitler thought it would break the hope of the British people. This was a great mistake, but not as much so as made in D-day.
When 2000 fighter planes and 700 medium bombers invaded Normandy, France in May 1944, Hitler should have been ready but he was not. He should have started sending more defenses to Normandy, and followed through on the plan that he and General Rommel agreed on. If he had done this, there would have been a better turnout. (Pearl & Shafter: Winds of Change) Hitler did not believe that the attack on the 7th army was the main invasion, and was expecting something bigger to come. Hitler was not allowing many of the divisions he had; to defend some of area's that needed defending. It only took a week for the allies to gain a solid front. Hitler made it easy for the allies to cross into Normandy, because Hitler did not send enough defenses.