I think it'll be Pakistan vs India to start off with, then China will join on Pakistan's side, then America will send troops to help out India, while Russia enters the conflict on China's and Pakistan's side because of the USA acting without the approval of the UN Security council (or more likely, going to war on India's side, after Russia and China both vetoed the action)
then other nations will enter, although I don't quite know where it'll end up, either way, many millions will die







