Why do countries have to cooperate in order for world trade and global competition to thrive?

That way if one Country, say, China, has a surplus of a certain item, say, rice, and the US has less of that and more, um . . . titanium than China, if they hadn't and refused to cooperate, than people in the US might starve, and foundations in China would topple and kill millions of people. If they cooperate, than those things would not happen.