This is the part of the community I don't get. As soon as something - anything - happens, everything suddenly becomes all peacenik. Why? Why stop fighting and do some peaceful migration? Why not throw everything at them now that you have nothing to lose?
This is the one area where BM could never match real life. In real life, when the going gets tough, people get more aggressive, not less.
In RL, you CAN totally destroy your enemies. And the survivors will not live long enough for revenge.
In this game, you can't do this. Many things are in place to make sure that people who don't want to die, can't. In fact, people who don't want to be touched, for the most part, can't. And player characters can live long enough to see a lot of nations rise and fall. Victors don't really write the history all that much.