Thinking about the Mageocracy vs Theocracy war made me think of new spells. What spells do you suppose exist in D&D that your typical war-wizard would know in order to help the Kings troops in battle vs another empire. One that I assumed would exist is a massive fog cloud type spell. Imagine fog breaking out from the Kings castle and spreading several miles in all directions - bring out the flying improved invisible mages now!!
If you still fought in formations I can imagine massive protection from elements and shielding type spells. Massive walls of animated tower shields, etc. I imagine most of the magic would be focused on supporting the infantryman since most "modern" stuff now supports the infantry and the grunt on the ground. There would probably be lots more defensive spells and team-casting rituals.
Fun to think about...

Fun to think about...