Slitherine

I recall this being raised as an issue around launch, and talk that it would be tweaked. I haven't played a huge amount since, so I'm not aware if it has been raised again.

I am turn 141 into a game as Apulia an Calabria (Now Kingdom of Sicily), I have two vassals, Pisa (opinion 99) and Firenze (opinion 51), and both control a single region each.

I have not received a single absorb vassal decision all game, so I have been unable to raise its priority. I have lowered the priority of most of the other decisions to the minimum.

My question is, what more can I do to improve my chances of getting the absorb vassal decision?

I feel the randomness of regional decisions and building is honestly the weakest part of the game. I appreciate that building randomness was partially addressed for this game, after FoG: Empires, but it is only a partial fix, which works for some factions but not others, because some factions are far more authority starved than others, so tying building choice to authority creates an unnatural advantage for certain factions, where it should not necessarily go.

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Authority gain is mandatory for all nations at some point, so a nation starved of Authority (and thus unable to use any edict) is a clear sign things are not going well. If you pick a backward or backyard nation, that would be normal, but those are difficult games—self-imposed challenges, not the norm.
As for the decisions, there is indeed the button Surt mentioned. And yes, with so many decisions, the system feels a bit too random. I’ll add something in the code to increase the chances of getting an “absorb vassal” decision when you actually have vassals.