That's not how a climatological shift works. The cities and empires don't die overnight, the descend into oblivion gradually. Maybe there's a war or two, but the end result is that the area is simply not inhabitable or viable in the way that it once was. As people leave, the kingdoms become ruins. It's happened a few times. You can't really prevent it, only adapt to the results.
Climate disaster is ten to twenty years away- and always will be.
That's not how a climatological shift works. The cities and empires don't die overnight, the descend into oblivion gradually. Maybe there's a war or two, but the end result is that the area is simply not inhabitable or viable in the way that it once was. As people leave, the kingdoms become ruins. It's happened a few times. You can't really prevent it, only adapt to the results.