OK, the US invasion of western Europe (well allied invasion) was a defensive war against someone else who started it.
Re-invading someone who fought the invasion in the first place is different.
The US (or anyone else) didn't just go and invade South Korea, Japan and Western Europe. They were attacked first.
What were the four thigns about Tibet? Mass migration, Trade, decades of miltrary investment/occupation, and a peaceful people.
Well Western Europe had instead, Trade, economic investment, and a peaceful people (at least they were peaceful toward the Americans because they had been rescued from the Nazis) No mass migration, so the cultural influence was done by TV and film, and Western Europe is not today as integrated into the American empire as Tibet is to China, so all in all a less successful subversion.
Now if you can get about four major factors then you might have another successful 'boots on the ground' mission.
The MAJOR one being peaceful/loving people. I bet the next nation the US invades will love the invaders, just like Iraq and Afghanistan before it. (sorry i'm assuming it will be the US, Russia recently invaded two places where the people did kinda love them, but they were mostly seperartists who claimed dual russian citizenship... i imgaine Puerto Rico would be the close-est US equivalent.)