I have to wonder if any first-world nation's army today would be able to take part in an aggressive action without some hesitation.
Suppose Biden sent American troops into Canada--would we see those troops be successful at boots-on-the-ground killing of Canadians? I kind of don't think so. I think we'd see some resistance that would come across as ineptness.
I think 21st century humanity has psychologically moved past the idea that killing--especially up close and personal--is something easy to do.
I think we have to have a really good reason. For example, I think our troops would be more successful fighting Iranian soldiers in the defense of the women they're killing over there.