Why does Europe need Nato?

It just seems to me that it would be better for the continent to form an alliance without the United States, I am not saying the EU should have its own Armed forces but something similar to NATO without the US yelling and screaming about this and that. Do you agree or disagree as NATO was supposed to be defensive in nature and not used to occupy other nations or get involved in affairs outside of its members borders. Agree? Why or Why not?