Meanwhile in Wei, the Sima clan, through years of political maneuvering, had ousted the imperial family from power and reduced the roles of the Wei emperors to mere figureheads. The Wei regent and de facto ruler, Sima Zhao, believed that a successful military campaign to reunify China would bolster his prestige and convince the imperial court that the Mandate of Heaven had fallen on the Sima family, which would minimize the opposition for a formal succession. Disturbed by Jiang Wei's constant harassments on the Wei border and aware of Shu's internal decay, Sima Zhao decided that the conquest of Shu would be a vital step in unifying All Under Heaven.