Equal or surpass the monster stance difficulty rating to enable extra benefits. Your equipped hero type determines the benefit and the hero stance power is determined by the sum of the hero level and same type heroes in allience with him.
Defensive alliences increase the critical stance bar which gives a flat percentage increase to the chance to get a critical hit. Offensive alliences increase the damage bar and the damage done by every attack. Balanced alliences reduce the rate at which the critical and damage bars decay. Damage added through these bars does not count towards the minimum threshold to receive rewards.