I need ideas for a story I'm writing.?

I'm writing a story for fun about some people that survive a nuclear fallout. I've got everything but how the fallout happened. For some reason I'm stuck on just this little part. I don't know if it could be about Korea shooting nukes because of what's been happening recently in hawaii, or the Russian's since they've been building nuclear weapons for a long time now, I just don't know what I should do. If there's any other idea's about a fallout go ahead and list them, like if it's not something that's currently going on in the world right now but a few years into the future perhaps, where technology hasn't changed much or whatever.

Any ideas are welcome even if it's not from a fallout, but some sort of Armageddon. Detailed idea's would be highly appreciated, thanks to all who answer!

Also, I've heard alot about China and America starting a war and ending up having a nuclear holocaust as the conclusion of the world.