How to provoke a war?

[scorillo]

How to provoke a war with neutral faction?

Just attack an army or a city. lol

[pezhetairoi]

Simply put, attacking an ally instantly means no other faction will ally with you because they see you for an oathbreaker. Apart from that, well, take the offensive to offend another neutral faction, because if you're not their natural enemy they probably won't attack you.

[gardibolt]

Is that true if you break off the alliance before attacking them? Or Once and Ally, Always an Ally in the AI's mind, at least as far as the player is concerned?

I've tried not to break alliances myself, but in the closing phases of my Julii campaign I've had no choice as there was no one left to attack but one of my allies. I canceled my alliance with Pontus and then attacked, since I had a full stack next to each of their cities. My other allies immediately cancelled their alliance with me, but haven't yet declared war. But they'll be the last ones on the board as soon as Pontus falls (momentarily) so, too bad for them.