Fifth sun casus belli and tributary system explained

Love the new update but having a lot of trouble unlocking tributary tech and wars

I can get claims on neighbors counties but this is not enough to unlock wars.

Also, I can't find the technology to unlock more direct control on tributaried. At one point I developed the tech for absolute tributary system but was still missing the middle one.

There are no boundary changes in the map so I don't think even the AI has been able to figure it out.