Then she rescues him and he says Americans are evil. That they're building a massive bomb that could kill millions then she sees it dropped twice when she goes out into the real world. Hoho the plot can take on any point really and she'll just side with whomever she saved first.
They'd have to re-work timelines since that's WW2 you're talking about. But based on the plot of this movie, we could say Ares is a live and well since WW2 occurred and many more atrocities on this planet.
Yeah, add in the internment camps for Japanese Americans and you've really got something. (Unless he tried to make Themyscira into a comfort women station, of course...)
You want to know something funny? This idea was actually addressed in the 70s Wonder Woman show with Lynda Carter. An alien came to Earth and asked her why she sided with the Americans. I think she said that she believed in American ideals, even though people are fallible and shamefully don't always live up their ideals.
I have to look that one up. Bashing America (and certain American leaders) has been popular (and sometimes well-deserved) for a long time now, but American ideals about liberty, freedom and equality are still viable and worth fighting for. We aspire to remain loyal to these ideals, not the Emperor, the President, Sharia, social media, or anything else likely to fall short of these ideals.