The situations aren't that similar. For one thing, in the ancient world there was a lot less global communication and traffic, so rome was the only advanced civilization that europeans generally knew anything about. The fall of rome by itself therefore was pretty much apocalyptic for europe.
It didn't affect china much at all, but china wasn't in any position to trade with or enlighten in europe if the us fell by itself, by contrast, there's lots of advanced nations all over the world that would ready and able to take a keen interest in that situation. There would probably be a lot of fighting, but I don't think there'd be what you'd all a dark age come out of that it would take a lot of advanced nations being destroyed all at once to really put the lights out generally. Of course that's not out of the question either.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.