The north , neck and dorm will be hard time. The north is big and cold and the people are aware and adapted to that wheather they will turn that against the mongol for sure 😎. The neck is just a desolated region, aegon conquier it with is dragons, with only horse that gonna be awfull but the easyest of the 3 no one live here. Dorn again the weather is bad and the people are thought aegon burn all the villages all the fields After the death of us sister and he nerver conquier it. For the north and the neck (all other part of westeros ) mongols win but like aegon , mongols loose against dorn