Erm, for the most part, yeah. There are exceptions, such as WW2 and some others which I'm probably forgetting. If Hitler had taken over Europe, and the odds of that happening were sharply increased without America involvement, then its pretty clear who would have been next. That was a legitimate case of pre-emption, because it was obvious that Hitler and his allies had both the will and the way to conquer everything in sight. These days, some may have the will, but no one (not even America) has the means to pull it off.
And not trying to be an asshole, but the war of 1812 started when a America tried to annex Canada, not the other way around. Actually, this is oversimplified, but it was the US who declared war first.