IMHO nukes are no longer the ultimate weapon. Bacteria are the ultimate weapon. Example: botulism. if you can contaminiate a food or water supply, it will kill 70% of those it infects. Or anthrax- released in an underground station during a winter sniffles episode, it's a near 100% unpleasant death sentence for everybody exposed. Or certain gastrointestinal diseases that are best left unnamed. Terrorists can strike quietly, cheaply and undetectably. A single determined terrorist with access to the material can paralyse a society. So even if you do nuke a city to glass, you only need one determined survivor to make your life hell.