I think there's a distinction between being involved in conflicts and being belligerent. Post fall of the Soviet Union the U.S. took on the role of world police, and that included getting involved in lots of conflicts that probably normally would have been fought by regional powers (ex. Desert Storm/Kuwait, Bosnia). The standout here of course is Iraq/Afghanistan, but in terms of globally belligerent behavior China seems to be the clear winner here, no (or maybe N. Korea but seems more regional)? Trying to redraw boundaries, creating artificial islands, aggressive maneuvers endangering Philippine and Japanese sailors, everything regarding Taiwan, aggressive trade tactics... the list goes on.