It has been primarily "Southwest Asia," that the United States has been militarily involved in the 1990s and into the early decades of the new millennium, since this qualifies as the "Middle East," where the US continues to fight terrorism.
Unity was brought mainly by the decades-long process of setting up and expanding the European Union in the aftermath of WW 2; also the disappearance of the Iron Curtain in 1989 was a major factor in uniting Europe.
Major disruptive factors were of course the two World Wars, and before 1989, the existence of a Communist-dominated Eastern Europe versus Western Europe.
