I've played two games on normal now where all I did with my caster hero was summon up one of each summon, and go on a rampage, killing every AI with that single stack of units.
You'd think after I wiped out a few civs, the remaining AIs might be more hostile towards me, but nope, no declarations of war, no hostility, just 'hi, nice to meet you!', then I walk in and kill their cities with the summoner stack.
I'll bump up the difficulty, but so far I have yet to even have an AI declare war on me, even when my military was otherwise weaker than theirs early in the game.