Stewie0416
Who Cares?
Has anyone ever been good friends with a sorta weak civ who was in a huge war with 6 civs? Then that weakling asks to become your vassal? You accept and now you're at war with 6 out of the 9 other civs in the world?
I took Bismarck under my wing and Brennus, Ragnar, Alexander, Justinian, Wang Kon, and Ghandi declared on me. Brennus was Raggy's master and Alex was Justin's master. I had NO idea that would happen or I would have just declared on Bismarck. Especially since everyone but Wang was friendly or pleased with me.
This was chieftan and I was Roosevelt (it was my first game on BtS) so it was a piece of cake taking over half the world. Weird as it is, I got a cultural victory.
So, has the first situation ever happened to you?
In a normal game, not really. I never really get ASKED take vassals, i usually "persuade" my vassals through "non-peaceful ways"

But this does happen to me a lot in Rhyes and Fall of Civilizations. I usually end up with 2-3 voluntary vassals and always there is one that is at war with the entire freaking world.

If we absolutely have to have this AI cheat then at the very least the rival should demand you end the war first, and only then declare. 