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.
(don't talk to me about muh pearl harbor, that's a blip compared to what happened in europe.)
so that's why i think (at least some) european countries are (at least somewhat) more hesitant to go out and intervene in the affairs of others