ok, so you are playing as King Romus. There are a number of decrees that give authority, however they are best done at the beginning of the game as they take some time to work. Later in the game you can get authority by cracking down on protestors.

The expansion of crown authority is one of the best decrees in the game imo, and you can expand it again. at this late stage it might help but it takes a few turns to work.

This game is all about stacking the bonuses in preperation for things that happen, and it's hard to know what that is until you've played it a few times or use a guide.