Checking originality of concept

Hey guys, I'm starting up a piece of fiction here, but before I get deep into it I need to make sure I'm not ripping off someone I've never heard of.  So has there ever been a novel based around the essential concept that the American Revolution failed, and that England controls the USA even today?

how about a book where Europe NEVER EXISTED. As in, the continent. just africa, australia, n/s america, antarctica, and the middle east (and part of where russia is)?

has that been done?