Why does it seem that based on Bush/GOP years, we Americans are much less inclined to invade another Country?

I believe you're question hasn't taken into account the reality of 20th Century World involvement. The US was loathe to engage in what was viewed as, "Europe's problem". We remained smug and safe; uring ourselves that "Fortress America"; aided by the Pacific and Atlantic Oceans; would prevent our becoming sullied by the conflicts that seemed to apply to "them". The US was an isolationist country right up to Pearl Harbor.