How quickly would you want to do this? I think I would prefer it it were over quickly, i.e. a certain number of bombs are spawned at once, 30 days later land is blighted, and then we know for sure we won't have any more for at least a year.
I fear the strategic implications of regularly spawning nuclear bomb would have on the general gameplay. Uncertainty creates fear in realm leaders, and many realms will prefer never to go to war for fear that their enemies would destroy their precious lands.
It would definitely have to be an event, i.e. something that happens once and then it's done.
