I'd suggest, in addition to the other options, the Moontide Quartet by David Hair.
It basically runs on the concept of a magocracy ruling one continent invading another continent periodically during a "Moon tide" when a land bridge is exposed to the open air. Customarily these invasions are Crusades, and they are led/run by magi. There's healing magi and logistical stuff, and there are also battle magi who just obliterate the foot troops of opposing forces.
