I just wish to relate what happened in my last campaign. I was so disappointed that it made me give up.
I was Skaven and had yet to accomplish the fourth ritual. I start mine, about 6 armies spawn in my region. I see the Elves start their one. I pay for an intervention army. My army spawn just near one of the cities which was part of the ritual. The city was poorly protected by a lord with about 6 units. I said to myself, cool, I will get rid of this city the next turn and it will interrupt the ritual. Next turn : my army doesn't attack and start to raid... Next turn, it goes away from the city and start attacking randomly little unimportant cities. WTF... 3 turns later, the lord who defended the city which was supposed to be attacked has now a complete army and my intervention force has lost about half of its troops being out of control. Ok I say to myself, I just have to wait for chaos to attack, the Elve has let unprotected one of the city which is part of the ritual. 7th turn, 8th turn, 9th turn. The computer NEVER was attacked by the chaos... My wish to finish the campaign just totally vanished.