Assuming the war in question is the classic "invasion" scenario everyone benefits from repelling the foreign invader who's coming for their resources, or alternatively the succesfull invader who has now a lot more land to cultivate and grow as a nation, which produces stability which produces wellbeing which leads to a better quality of life in general.
I mean, even the lowliest footmen benefits from the enemy's lowliest footmen not reaching his hometown and razing it.