Hard to say, sometimes i see i have high relation ship but still AI refused it, but normally any relation above 100 should clearly good starting point to do any kind of treaties, usually u need offer money they will agree for it.
I created hard so the AI dont simply build alliance in turn 1 , anyways i think i give cold blood trait to hun, since most of their army spawn in snowy region, its seem there is correlation between undamaged forces vs damage forces in term of city attack probability.
The theory itself the fresh the troop the higher the chance its didnt do raiding