It aims at peace yes, but importantly it is an inter-national organisation, meaning it lives beside nations and doesn't have any formal power over them. In some cases the individual treaties negotiated at the UN result in the UN having some formal influence over member nations, but even then the concrete commitments are usually very limited. For examy the Paris agreement basically just says you have to make a few reports, with peer pressure being most of the enforcement.

In contrast the EU is (partially) a supernational organisation: in some fields the EU holds formal power over what happens in the member nations (because the member nations changed their national law to give EU that power).