instant unrequested vassalization

[estebancastellino]

hi everyone.
I'm Savoy and together with my ally Milano went to war againt the swiss and their ally 3Leagues. Made separate peace with 3Leagues: sacked city, brake alliance with the swiss. Peace deal with Switzerland: gave their 3 romandie provinces to Milano and vassalization.
A year went away and out of nowhere, the 3Leagues become my vassal. How? Why? No event, no pop-up, nothing. I was just playing and suddenly I'm over my diplo relations. When I check, the 3L are my vassal.
Context:
-I have permanent claims on all Switzerland via mission tree (integrated Geneve).
-Switzerland does not have cores yet on the area via mission.
-I do not have dominering attitude towards 3L nor good relations. Their total development it's 15 between their 2 provinces, nor do I have their provinces marked as of vital interest.
-yes, the plan was to aks cores back from my ally via favors and then reconquer cores from 3L once Switzerland gets them from mission but I'm not there yet.

Anyway, I wanted to share this since it's most curious and I cannot explain. Maybe 3L triggered and event but I had no notification. It's odd. Good luck everyone.

[Medicles]

A swiss event can trigger when Three Leagues has 100 opinion of Switzerland, which gives Switzerland two options, one of which is the free vassalisation of Three Leagues when Switzerland has finished the "Consolidate Switzerland" mission, which is extremely easy done, even by ai.

So i highly assume that event happened, Switzerland chose vassalisation and you got the vassal.

[estebancastellino]

Sure! makes sense. I know about that event but never occurred to me that it could be the case. Well done sir and thank you very much.