For a long game: hide from enemy heroes and gather troops in dwellings. They won't go near the Dungeon. Also, destroy a couple of castles. Then gather your forces and finish off the last one. No one will bother you anymore.
But if you're playing on "Hero" or "Veteran," my advice is to lower the difficulty. Then everything will be quite manageable. On "Recruit," I cleared the entire map.
Цикл "Закадычные враги": "Особенное гостеприимство, "Супероружие", "Меж молотом и наковальней"
"Падение Шантири"
Кампания для "Кодекса Войны"
"Выбор Сагиттеля"