During the Sino-Soviet split, strained relations between China and the USSR resulted in bloody border clashes and mutual backing for the opponent's enemies. China and Afghanistan had neutral relations with each other during the King's rule. When the pro-Soviet Afghan Communists seized power in Afghanistan in 1978, relations between China and the Afghan communists quickly turned hostile. The Afghan pro-Soviet communists supported China's then-enemy Vietnam and blamed China for supporting Afghan anti-communist militants. China responded to the Soviet war in Afghanistan by supporting the mujahideen and ramping up their military presence near Afghanistan in Xinjiang. China acquired military equipment from America to defend itself from Soviet attack. At the same time relations with the United States had cooled considerably that by 1980 Washington had begun to supply China with a variety of weapons. They even reached an agreement of two joint tracking and listening stations in Xinjiang.