What Were The Reasons For The Defeat Of Germany In World War 2?

1)Too ambitious - Hitler's lebensraum policy stretched the military from its base of operations in Germany. They were ill prepared and equipped to fight in Russia so far away from home.
2) Miscalculations - Germany did not anticipate the strength of the US or the Soviets. The US had resources, the Soviets had numbers. Over time, Germany became exhausted by their resiliency.
3) No allies - Germany had no real strong allies by 1943. Italy had surrendered; Japan was mired in a Pacific war.
4) Putting too many resources the "final solution" - concentration camps required a massive amount of bureaucratic, human, and material resources. These took away from the war effort.
5) Inability to capitalize on technology - Germany designed rockets, the jet engine and nuclear weapons. The war ended before they could be used to any significant degree.
6) The allies air power - preliminary bombings of Normandy softened Germany up for an amphibian invasion. After the success of Normandy, bombing continued in advance of a ground assault.
7) Contrasting leadership - Allied leadership was better organized and energized to finish the war. Eisenhower, Patton, McArthur, Churchill, Stalin created morale and used experience to succeed (Dieppe as a training mission). The German leadership lost faith in Hitler and abandoned the war effort in favour of liquidating concentration camps and escaping to tropical locations. The public no longer supported the war as infrastructure was destroyed by allied attacks.

* Some notes from a Canadian History teacher.

There are several pivotal moments that caused Germany defeat in World War 2.  Not conquering or making peace with England, becoming allies with Japan and then after Pearl Harbor, declaring war the USA and opening a second front by attacking the Soviets were the dominant reasons why Germany lost WWII.  
However another reason why Germany lost the war I think  and that is often overlooked is the wild card that was Mussolini.  Italy, after Germany's initial success at the early stages of the war, attempted to capitalize on the Allies misfortunes.  Especially in the case of England.  Mussolini, envisioned a new Roman Empire, and feeling that England was preoccupied by Germany, felt it's colonies in Africa were easy pickings.  After initial success the Italians were in full retreat in Africa.  Also, Mussolini, without Hitler's knowledge or his approval attempted to invade Greece.  They were soundly defeated and forced to retreat.  In both cases Hitler had to intervene by sending precious men and materials to conflicts he did not want.  These occurred as the plans for the invasion of the Soviet Union were being drafted.  
Because of diverting resources to conflicts in North Africa and Greece and the invasion of Yugoslavia, the invasion of the Soviet Union was delayed from mid-May until mid-June.  The German army would live to regret the delay by being mired in mud and fighting to within sight of Moscow as the dead of winter set in.  
Without the delay and the freeing up of men and material, Hitler might have been able to force Stalin to sue for peace.

The country had been bombed to bits. All of their cities were totally destroyed. The Germans had to rebuild their country and got no help. Now remember this when Haiti is 90% destroyed from a little earthquake.

Destroyed infrastructure and a leader who was increasingly insane. It's a little known fact that hitler was prescribed cocaine, in eye-drops, by his personal physician. This may possibly have had something to do with him attacking russia, but he really woke up the bear when he did that, and created new enemies that he was unable to deal with.

also, previous experiences, even incomplete experiences that he didn't truly learn from, galvanized his opinions sometimes. An example is when the german troops wanted the world's first assault rifle, the STG44, and he thought it didn't have the range- based on his experience in ww1, where he was removed as a casualty relatively quickly because of an artillery strike.

there are many details, but first, germany running out of money, then running out of allies, and then being bombed into submission by the allied powers- not that the bombs were to kill, they were to destroy infrastructure, such as factories and railroads, so that germany, eg, couldn't make tanks, or ball bearings, or ammunition.

add to this how evil they made themselves, and how it galvanized everyone against them, and you'll see why everyone kept fighting them long after they'd have given up otherwise. Normandy, bastogne, etc were all accomplished because the germans made themselves into these monsters that were so easy to hate.