<The reasons why Kashmir is in India and not Pakistan are complex, and reflect no credit whatsoever on the British government of the day that drew up the borders:(

Quite right. I'd hate to have to count the number of wars that can be chalked up to a bunch of guys in a clubroom drawing on a map with a magic marker. And Britain, although obviously in this position quite a bit due to its former huge array of colonies, is certainly not the only culprit.

On the other hand, I'm not sure how else such borders would have been drawn without being somewhat arbitrary about it. If you asked the opinions of the inhabitants before drawing a border, each side would enthusiastically support drawing the border on the far side of the opposing nation, and you're back to square one.

As for nukes, I don't know exactly how many working warheads each side has. If each fires off a few, the human tragedy would be immense, but there would be little global effect. Keep in mind that we fired off hundreds of atmospheric tests over the past fifty years, and by golly, we're still here.

The small silver lining in that mushroom cloud would be a worldwide exposure to the human and property damage of a nuclear attack, in CNN real time, which would make an enormous impression on people about how bad these weapons are. The first nation to fire off one of these on a populated target would get a lot of negative political backlash.