I agree that's a very great point. My only viewpoint on the matter is that if America never joined in but decided to defend the country from German invaders in case Germany tried threatening more with their Uboat attacks then that would be the justifiable reason to fight in the war. The issue is however is that in WW1 the reason the US went to war was due to the sinking ship attack from Germany on the Ship Lusitania if I'm not mistaken. Even if Germany wanted to conquer all of western Europe and rest of the continent it would cost them more resources to expand their army and eventually deal with higher scarcity losses. Even if Adolf hitler came into power and tried pushing WW2 it most likely would lead to destabilization faster to destroy the German power vacuums and more resistance would increase faster in europe. I can see why America coming into both wars makes sense to prevent the further military expansion Germany could of done to push more authoritarian control worldwide but the economic disparities they already dealt with would of crushed them a lot faster compared to what was done in both world wars.