China
india only win
no china has much more men
The US and China are not at war so this question is unanswerable.
China would win the war again because it has more soldiers, more money to pay for the weapons, and more land to train on. It also has a better technology than India, and also more allies.
pakistan wins
Russia. They have way more nukes then China.
No one would win especially if either of them uses nuclear weapons. The whole world will lose.
India and Nepal currently have very good relations and a war between them is highly unlikely. That being said, India would win a war with Nepal quite easily since its military is much larger and much better equipped.
In such a war, it is safe to assume that China would be attacking and India defending. The Chinese would certainly have the quantitative advantage, but they would have to negotiate some of the world's most mountainous terrain which would favor the Indians' defense. I think India could handle such an invasion on its own, but if not India would certainly be offered help from non-Communist countries around the world. It is doubtful that China would play its nuclear card because India has nuclear weapons too. The Chinese know all this, which is probably why this war has not happened yet.
INDIA
Without either side using their nuclear weapons, and with the Indian Army resisting a Chinese Army invasion, I think India would have a good chance of winning. If it were the other way around China would win, but India would have little reason to invade China.