World War III: America and the Soviets nuke large chunks of the world and destroy any semblance of international order. Violence and War are seen as normal and nessicery for survival in the shattered world.
Yeah, the most/probably only likely scenario is WWIII with the Soviets. That could fuel a rightward shift amongst non-Communist nations. I can't imagine the Royal Family ever regaining the kind of power they had before they surrendered but they might end up with a little more real power than in OTL. Something along the lines of the Queen of England, but with tradition mostly restraining them from using it.