That may be. I was attacking Toria, which is their capital. Well, if taking a capital causes a dogpile, that is something a player might be interested in knowing! Of course knowing whether it might be or whether it will in a particular instance would be useful also.
Yes I checked and Toria just fell to my control. Of course a lot of my trade routes have disappeared as well, fortunately I had many trade routes to minor factions. Probably those trade routes will be plundered shortly. So I just need to go back and don't siege Toria.
It seems a little ridiculous though. All the diplomatic effort I have been making is just swept into the wastebasket. Hmm, I noticed that one faction didn't DOW - the one I was allied with. Perhaps I should scoop up some more allies also.