Vassalage

[Muramasa1794]

How do force another faction to be my vassal?

[Antiokhos Euergetes]

You will need to beat them a good few times and then it's not always guaranteed. But if you truly think you earned it, use force diplomacy.
The AI Ottomans in my campaign have vassalised Serbia and Ragusa

[Kranos]

I never seen this option. I defeated Ottomans and Hungarians lots of times, almost for the entire duration of my campaign but this option doesn't appear in the diplomatic demands. Played both campaigns versions of the mod.

[Antiokhos Euergetes]

I just started a new Albania campaign on vh and on turn three the Venentians asked me to become a vassal