Mid Game+ magic.

[sushiboat]

I concentrate mostly on Conjuration and Construction to get SC's, SC equipment, unbreakable troops (e.g., Vine Ogres, undead, constructs), and eventually, artifacts. I will split off a small percentage of research points to bring other magic schools to at least level 2. You get Acashic Record at Conjuration 5 for searching your most secure provinces. (Don't waste it on a province that an enemy might be able to capture and hold for a long time.)

For Blood nations, research in Blood substitutes for Conjuration, at least until Blood 5 (Ice Devils).