" As the power behind the throne, the Fujiwaras not only maneuvered the young emperors into marrying their own aunts but ensured that emperors abdicated at an early age, so that each emperor was a young man easily manipulated by the family’s elders. Thus the emperor himself had little real authority. To “capture the king”—to have the emperor father a son with one’s daughter—was the route to political power in the Japanese court . "
― Stephanie Coontz , Marriage, a History: From Obedience to Intimacy or How Love Conquered Marriage