There were a number of reasons for the defeat of the Axis Power in the Second World War : 

The German army was regarded as invincible at the initial stage of the war, but the myth gradually came to an end. At first, the Allied Powers could not understand how to cope with the German Blitzkrieg. But very soon they realized from their early failures how to tackle this problem. The Allied Powers under-stood the importance of air support and air carriers. With superior air and naval power, they won the battles of Atlantic and the Pacific. 

The basic weakness of the Axis Powers was their shortage of rubber, cotton, nickel and, after mid-1994, oil. To win the war, constant supply of raw materials were urgently needed and in this point, the Axis Powers were very much handicapped. 

It was very difficult for the Axis Powers to contest with the combined resources of the USA, USSR and the British Empire. In Germany’s case, Mussolini was partly a burden because of his incompetence. This became a constant drain on Hitler’s resources. On the other side, the Soviet Russia reconstructed their industries and continued production to a large extent. It has been estimated that by 1944 Russia had four times as many tanks as the Germans and could put twice as many men in the field. America manufactured over 70,000 tanks and 1,20,000 air crafts a year with which the Germans and the Japanese could not compete at all.