A. He formed the church of England and made himself the head.
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.
