I think that going to war just because of "getting more lands" or something like that is just dumb. We are roleplaying after all, not playing Victoria 2 or Hearts of Iron 3. We are supposed to tell a story about our nations, not go to war with each other after finishing a THIRD WORLD WAR.
We could do a second Cold War between Britain and other countries not affected by the Third World War. Instead of a Fourth World War. If this nation roleplay is going to turn into a Fallout-based nation roleplay, then I will be disappointed with you guys.
It's stylized as a crusade against Islamic extremism. Still, you have a point. This serves more use as a crisis to provoke international discussion than an actual war. I would recommend declaring by executive GM order that this war can't go nuclear, @MetalLover. In future, sure, but a nuclear war right out the gate is a bit silly.
I'm officially co-GM but I believe a decision of that importance isn't mine to make.