Actually, I think America has always used restraint. If we crashed into Mexico or Canada with 3 divisions, that would be lack of restraint. Napoleon showed lack of restraint. Hitler showed lack of restraint. America has never been like that.
I had that argument with a liberal once. He was comparing the US to imperial Rome. This was, of course, during the Bush years. I told him if we were what he described, we would, have rolled through Mexico in maybe a short week. Canada, probably two weeks.