By the mid-13th century, the problem had worsened considerably. The Upper Burma heartland over which Pagan exercised most political control had run out of easily reclaimed irrigable tracts. Yet their fervent desire to accumulate religious merit for better reincarnations made it impossible for Pagan kings to halt entirely their own or other courtiers' donations. The crown did try to reclaim some of these lands by periodically purging the clergy in the name of Buddhist purification, and seizing previously donated lands. Although some of the reclamation efforts were successful, powerful Buddhist clergy by and large successfully resisted such attempts. Ultimately, the rate of reclamation fell behind the rate at which such lands were dedicated to the "sangha". (The problem was exacerbated to a smaller degree by powerful ministers, who exploited succession disputes and accumulated their own lands at the expense of the crown.) By 1280, between one and two-thirds of Upper Burma's cultivatable land had been donated to religion. Thus the throne lost resources needed to retain the loyalty of courtiers and military servicemen, inviting a vicious circle of internal disorders and external challenges by Mons, Mongols and Shans.