Most powerful mages don't care about war
When you have that much power, you're probably as motivated to fight or rule those weak nomages as the average person is to stomp on some ants or own an ant farm. Not even to mention following their orders (unless of course you're only making them think they're in charge, but that's still kind of boring).
Much like humans with nature, the more kind mages see nomages as weak and needing to be protected (from other mages usually, but also sometimes from natural disasters or themselves).
Most mages keep to themselves or mostly associate with other mages. Those that do integrate into regular society do so because they just want to live a (mostly) "normal" life and thus don't get involved in wars.
The Council of Mages disallows warmages from fighting in wars
There are the occasional bad apples that seek to rule or destroy everything, and that (along with some other reasons) is why The Council of Mages was started.
Powerful magic can be sensed by other mages from far away, and there are Council sects, agents and loyalists scattered all across the world to check for, report and/or deal with mages casting less powerful but still destructive magic. Every mage knows they'll be before The Council to face consequences in a few days at most if they start killing people left and right or casting mass protection spells to help one side in a war.