Strange stuff happened in my game

[alexo22]

I'm playing as Prussia in ~1670. I have Habsburg emperor, French king, duke of Hesse-Kassel and Duke of Luneburg as allies. I'm one of the great powers so are France and Austria.
All of a sudden, most of my allies change their attitude towards me to "domineering" and because of that their evaluation of alliance with me gets -1000 and they break the alliance.
I could understand why France do that because they are much strong than me. Maybe I could understand why Austria does that even though we have about the same strength (development, army size, technology etc). Maybe because they are the emperor. But why small 4-province Hesse-Kassel does that? How they could dominate my 550-development state with their 67 development?
Bug or feature?

 

[InvisibleBison]

Did you recently introduce a new heir? Doing so gives every nation you have a royal marriage with a CB to force you into a personal union, and the AI will automatically become domineering while it has such a CB, regardless of its ability to actually win the war.

 

[alexo22]

Did you recently introduce a new heir? Doing so gives every nation you have a royal marriage with a CB to force you into a personal union, and the AI will automatically become domineering while it has such a CB, regardless of its ability to actually win the war.

Oh yeah, I did that. Thank you for explanation, now everything is clear.