I was playing the Samnite War again, as Samnites.
As Rome I played it several times, and against the AI I never fail to win: just beat the enemy armies out of existence with your concentrated Legions.
As Samnites I won once - after giving up several times - when Rome surrendered in an Assault by a relatively weak Etruscan army, although I still don't understand why: isn't Rome a level 3 fort that cannot be assaulted?
Anyway, this time I tried to be careful not to trigger a Dictator with its additional armies, as I feel the Etruscans and Samnites can just about hold out defensively against a consular army. They can take level one fortresses by assault, but when you siege a higher level fortress, the Romans will eventually come with enough legions to beat you.
However, after a year of holding my ground against the Romans, they still got their Dictator, and now it is all going downhill.
So what exactly does trigger a dictator option in this war (and the other wars, probably they all have slightly different conditions)?
My experience so far:
Attacking Neapoli or Capua or Roma with the combined Samnite army does, attacking Velia doesn't.
Conquering Populonia with the Etruscans doesn't.
I did raise all strong infantry units available. Maybe this increased number triggers something?