This really is a great question! Thank you for prodding me think about this. There are no simple answers. For a dictionary definition of peace, see http://en.wiktionary.org/wiki/peace.
There are several different contexts in which people use the word peace. Some of these are:
I think that any one individual can only really feel at peace, if that individual is at peace with himself or herself. How to arrive at that inner peace is a different journey for every person depending on one's real and perceived needs.
Competition for a scarce or unique resource will result in conflict unless all competitors choose and accept the same non-violent way of resolving the conflict. Arriving at that consensus is not easy.
Given that we live in a world that has scare resources and people who do not always share the same values and do not all think the same way, I think that any one individual can only really expect is to be peace with himself or herself.
I think that we all want more than just that. Maybe that is the problem. Inner-peace, I think, is the only logically possible solution to that impossible want.
Do I have real inner peace? No! I am trying? Yes! Doing that can be trying. :-)