With Docm's logic, American soldiers were intentionally fighting for American imperialism and FDR's warmongering bloodthirst. What about allied warcrimes? Not saying this to make anything the OKW and others did any less, but the victor is easily forgiven.
No Axis country would have EVER invaded mainland US or Canada. Too much sea and even if the Axis won in Europe and Asia, they would've had to rebuild and recuperate and deal with all the shitty politics that was going on, such as keeping allies and maintaining puppet states. There was a lot of partisans very much active in Axis occupied Europe. Hell, even Germany was ill-suited for war in 1939. Their aircraft were already outdated and they had a slim selection of shoddy tanks, with most of their force being "liberated" Czech tanks.
A very large portion of German soldiers in WWII were foreign, including Volksdeutsch (From a large assortment of nationalities), Czechs, Slovakians, and Spanish... in the Wehrmacht. Not to mention the 20-30 foreign divisions of SS "Freiwillige". A common phrase I've heard from many first person accounts and interviews in many different ways are, "We fought the Bolsheviks to keep Communism out of Europe." Many American-captured Germans were being trained and rearmed by orders from Patton to prepare to fight the Russians, however we all know what played out: immediate Cold War. Early on, that was just the people being swindled into Hitler's grand speeches, taking revenge on the French and English in a matter of pride and shoving the pain of losing WWI back on their conquerors. For Poland it was also supremely nationalistic, restoring Prussia and yes - recolonizing the "German lands" they were expelled from after WWI.
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Did America win WWII alone? Fuck no. Any half-wit knows that's bullshit. However, the American contributions both militarily and industrially were huge. Main point being the lend-lease programs to the UK and Russia, helping feed millions of Russian soldiers who would've probably starved with their communication networks being crushed early in Barbarossa and the winter of '41. They also helped clothe and supply the Russians with heavy weapons, paled in comparison to when the T-34 began in full production, its design being revolutionary both on the battlefield as well as in the factory plant.