none of the two worldwars took place on US soil, and the US entered both conflicts relatively late, so there is less US cultural knowledge about them (mostly in the form of “relative X went overseas and died/came back traumatized”). but in europe, the countries were the place the WWs were happening. and they experienced a different way how those conflicts came to play: countries interfering in the affairs of other countries.
on the other hand, the US comes in and there's already a conflict going on elsewhere, it's not quite clear why it's happening, but it looks like it's bad, so “we can go over there and shut up the bad guys” *star spangled banner blares*