Define "Made peace". I'm unaware of such a thing in the code. Perhaps this was something Turock implemented. I'm not sure.
Unless you mean Clan wise. Then yes. When you set a clan to ally with you, you can't attack them. Otherwise, just de-ally them and attack them only a bit for land. Ally is useful as long as both sides agree to use it for such time and respect the agreement. Otherwise, just go back to normal, and de-war them and play as usual.
Nami kotogotoku, waga tate to nare. Ikazuchi kotogotoku, waga yaiba to nare. Sōgyo no Kotowari!
波悉く我が盾となれ雷悉く我が刃となれ,双魚の理 !
Every wave be my shield, every lightning become my blade!