Yes, the United States and the other Western Powers played a role in WWII. The Eastern Front had 80% of the total combat in WWII contained within it, however. The absolute scale is massively different. This was by design, however. Harry Truman gave the game away:

If we see that Germany is winning we ought to help Russia, and if Russia is winning we ought to help Germany, and that way let them kill as many as possible, although I don’t want to see Hitler victorious under any circumstances.

Essentially, the Western Powers hated both the Communists and the Nazis, and allied in a manner that involved the most bloodshed on the Eastern Front as possible. That being said, they didn't ally with the Nazis as the Nazis wanted to colonize Western Europe and the rest of the world, the West did not want to be subject to the same force of extraction they used to plunder the Global South, like the UK with India.