I've lost my last 4 games when an opponent I'd whittled down then proceeded to become the vassal of a friend I couldn't or didn't want to take. Each time, said friend had done not a bloody thing in the war except join it after I'd done all the work, beaten up the stacks, finally started taking cities, get 1 or 2 of them, then my friend joins and 2 or 3 turns later, vassal! Then my economy is behind from all the fighting and having my towns pillaged, I didn't take enough towns to get any room to breathe around them with the enemy culture encroaching so they're useless cities, and I never quite catch back up.
I believe there's an option to turn off vassaling, but I don't really want to do that. Are there any hidden mechanics behind this I can take advantage of to prevent it, or make my enemy my vassal instead? I always seem to be behind that friend in military power when it happens as I've been fighting for 50 turns while they sat there unwilling to even be bribed into the war despite huge power advantages and being worst enemies of my enemy. I'll often be about 10-20% higher in power than my enemy, but 40-70% behind my friend when the vassaling occurs.
I believe there's an option to turn off vassaling, but I don't really want to do that. Are there any hidden mechanics behind this I can take advantage of to prevent it, or make my enemy my vassal instead? I always seem to be behind that friend in military power when it happens as I've been fighting for 50 turns while they sat there unwilling to even be bribed into the war despite huge power advantages and being worst enemies of my enemy. I'll often be about 10-20% higher in power than my enemy, but 40-70% behind my friend when the vassaling occurs.