With the difficulty cranked up too :/ In just about 100 turns
Against 7 AIs 
I didn't even build my starting city, I just set out immediately looking for enemies to conquer, while researching Warfare techs once I took a city, then building troops in captured settlements.
This actually turns the strength of higher difficulty AI against them, as you acquire more developed cities than you could build yourself!
edit: It's also broken because each fight you win gives you the gold you need to buy more stacks of troops, which are perfectly strong enough with the warfare research that you acquire. Why wait for money when you can murder for it?


He might be ugly, insane, stupid, and generally a horrible person, but he sure beats up dem guyz gud.
It's pretty clear that the game balance + AI isn't in a state to handle abusive builds/tactics just yet.
This did expose another serious flaw with the current Sovereign death system though - because you lose the game if your Sovereign dies in enemy territory, and this applies to the AI, you can abuse the hell out of this against the AI - find the enemy Sov, take a nearby city to make it 'enemy territory', kill the Sov, voila, you just wiped out their entire empire, regardless of how large it was or how comparatively weak you are.
Sov death needs to result in timed banishment, or the ascension of a child as your new lord (which might do something to tie the dynasty system into the gameplay more firmly), it should absolutely not result in the instant removal of an entire kingdom (and all of their attendant cities magically vanishing into the ether).
edit again: Another conclusion - DON'T set the WORLD difficulty above Normal. I'm almost positive it's screwing over the AI, as several of them were wiped out very quickly. Crank up the AI difficulty and the number of AIs, but not the world difficulty (given the way the monster spawning system is working right now, I don't think you'd want to do that anyway).