Although peace would be the best solution, Joshua is right, waging war against the White legs is the best thing for Zion, everyone gets good thing out of it besides Daniel. It's a shame for him, but wishing only for peace will only bring disappointment in the end.
Retreat might have been a better option if the White Legs just wanted the land or the tribe's resources. That wasn't the case though- they wanted to completely wipe out both tribes, which means I side with Joshua on the issue. The White Legs can't be appeased, bargained with or anything- they just want to kill everybody. That type of enemy must be destroyed for the safety of everybody else.