Captured city won't advance levels

if this was whats known as a minor race city (usually has a guardian unit like pack dragon for example) then they never advance above level one in beta 4 at least... so i usually destroy and build my  own near the site if it had good resources near it..

Nah, it wasn't a minor faction, unless they have Sovs too.  I defeated the Sov a few turns before, and he escaped to the city.  I ended up fighting the Sov again, his spouse, and 1 or 2 starter combat units.  I forget what faction it was, but they didn't do squat during the game.  The Sov just stood there right above the city turn after turn.

Edit - Forgot I had a savegame at the start.  The leader's name is Yoren, from the faction Val'Diri - whoever that is.  So I guess that was a minor after all.  So... guess I'll leave that city undefended, in hopes some bandits come and take it down.