The three major allies army contributed significantly
The United States army was instrumental in liberating Europe through its military operations in France, Netherlands, Italy, Netherlands, and other important parts of Western Europe. When Europe was liberated, the United States focused on Japan and ending the final axis power that was still in the war even though others were defeated
It could be argued that the Soviets made the largest military contribution of all because of the amount of soldiers that they lost. They managed to beat Germany and liberate the Soviet Union, as well as Eastern Europe before heading to Germany and successfully taking Berlin. They were also prepared to help in liberating Japan.
The British army tried at first to help in France but when their help was repealed they had to wait for other allies to help. When Soviets and Americans came, British joined the fight in Europe, but mostly they are known for liberating Northern Africa which was completely under Axis rule. They had numerous famous battles and managed to beat Romell, a famous military general.
