What is the true purpose of Iarq Invasion? What is the purpose of US Bases in japan,korea and lot more places?

We are the worlds police. We need to be in korea to babysit them and make sure they play right. We have bases all over the world so it is that much easier to get to the country that is acting up. Are we right for doing that? I hope so or the world would be in trouble, or is it already in trouble????