By the end of the period, indigenous revolts amongst Khmer territories in Siam and Vietnam, and external attack from the independent kingdom of Champa, sapped Khmer strength. After the sack of the Khmer capital Angkor Wat by Champa forces in 1178–79, Khmer's ability to control its wider territories diminished rapidly. The first Siamese kingdom to gain independence, Sukhothai, soon joined to the newly independent Ayutthaya kingdom in 1350. After 1352 Ayutthaya became the main rival to the failing Khmer empire, leading to Ayutthayan conquest of the Khmer in 1431.