re: UK PM May invokes June election

It's just a quirk of the Parliamentary election system that they don't have regularly timed elections. I think they're supposed to hold them at least once every 5 years, but the PM can call for snap elections at any time (which often happens when there's a hung Parliament). Also, the UK went from 1935 to 1945 without an election during WWII, unlike the U.S.