This wouldn't seem to have a point to me (as you could make such treaties out of game anyway); unless: you could stipulate conditions for signing the peace trip. For instance, if you make war with someone and they propose to trade you X resources, etc., in exchange for peace.
But I don't really think there should be a system in the game for punishing people who break treaties. I believe that other players could attack them regardless of a treaty system, etc. But a 'treaty' to cease hostilities for x amount of time in exchange for resources would be cool - if unenforcible. (I.E. I wouldn't want the game to force them to actually adhere to it.)
"He uttered the word of curse, crush him with our Orcish iron!"