I don't really Luke the apocalypse idea, no offense, because it feels like it would turn more into horror than romance. Okay, hear me out, World War 2. I think it would be cool, most people know the aspects of it. I would say World War 3, but it would get difficult with the details and everything. I feel like any War in general wouldn't really do well because you have the side most people think are good, and no one would want to be on the bad side.
I like the alternate Earth idea. That way it still has aspects from real life, but not real life.
Okay, what if it is a space romance. Like a Star Wars ripoff about romance. I dunno. But if we are doing it on earth, or a similar earth, my character is going to be from Canada if we are not already in Canada.