i had a great campaign with the julii and now i have about 46 settlements including Rome.

But now i can't fight the Brutii because the message appears: can't attack ally because you don't have enough popularity with the masses.
Now they are attacking my settlements and i can't attack them, anyone know why?

Couple of turns ago SPQR declared all roman factions to be traitors and immediately i conquered Rome because i had 3 waiting armies next to it.
After that i kicked the Scipi out of italy.