How much does it cost to be a vassal?

[SadCat]

Cost, I do not know. I was back stabbed about every 10 turns. I would see them coming down to my city and would run my army up there to defend. They would besiege my city. Then I would hit them the next turn. After driving them off, they would offer me the chance to be a vassal again. This went on for ever or so it felt. When my defending army was recovered it would run down to take a new city. Then get ready to run back up for the backstab. After taking 5 cities this way I was ready to get my 2nt Army. That backstab was fatal for them. SadCat

[Death is yonder]

Read this excellent guide to vassalage made by jong-https://forums.totalwar.org/vb/showthread.php?t=83011