I am currently playing a Julii campaign (in the original game, not the remaster) and have been making good progress. About 30 turns ago the Senate decided the Brutii were getting too powerful but decided to outlaw not only the Brutii, but all three roman factions. Consequently, I was in a state of war with the Senate and the Brutii. The Scipii on the other hand were still in alliance with me. I sought to maintain the alliance as to avoid having to fight on two fronts. After a few more turns I took Rome and the Senate was no more. Fast forward to today I have finished pushing the Brutii out of Greece and the Scipii have started to attack my cities in Italy. The alliance at some point fell through but we are still neutral. Whenever I try to attack them the game tells me I don't have enough popular support to attack a neutral faction. Thus enabling the Scipii to take as many cities as they want and disabling my ability to prevent that.

I have done some research and found that this is a bug. I have tried various methods to resolve this. I've tried spamming low ranking assassins to kill their diplomats, generals, faction leader, or faction heir and each time such assassination fails they fail to see that I am behind it and thus declare war. I've tried cheating with scripts to give myself more cities to raise popularity, that does not appear to work either. (And I can't gauge the popularity value because the Senate tab has been unreachable ever since I killed them.) I was able to negotiate a new alliance with them, only to have them attack the very next turn, I tried breaking that alliance and still am unable to attack this "neutral" faction.

I am told this bug is extremely rare but this being the first full campaign I've played in this game, I have to consider the possibility that this will likely happen again. I would like to try to edit the save game to set the diplomatic relationship to "at war" if such is possible, but I don't know how to open the file in a readable format. If any help regarding this solution or suggestions for any other can be given, I would much appreciate it.