Next, Donyo Dorje, the Bönpo king of Beri in Kham was found writing to the Tsangpa king in Shigatse to propose a co-ordinated 'pincer attack' on the Lhasa Gelugpa monasteries from east and west, seeking to utterly destroy them once and for all. The intercepted letter was sent to Güshi Khan who used it as a pretext to invade central Tibet in 1639 to attack them both, the Bönpo and the Tsangpa. By 1641 he had defeated Donyo Dorje and his allies in Kham and then he marched on Shigatse where after laying siege to their strongholds he defeated Karma Tenkyong, broke the power of the Tsang Karma Kagyu in 1642 and ended the Tsangpa dynasty.