Compounding economic difficulties were new military challenges. In the late 1970s, Cambodia under the Khmer Rouge regime started harassing and raiding Vietnamese villages at the common border. To neutralize the threat, PAVN invaded Cambodia in 1978 and overran its capital of Phnom Penh, driving out the incumbent Khmer Rouge regime. In response, as an action to support the pro-Beijing Khmer Rouge regime, China increased its pressure on Vietnam, and sent troops into Northern Vietnam in 1979 to "punish" Vietnam. Relations between the two countries had been deteriorating for some time. Territorial disagreements along the border and in the South China Sea that had remained dormant during the Vietnam War were revived at the war's end, and a postwar campaign engineered by Hanoi against the ethnic Chinese Hoa community elicited a strong protest from Beijing. China was displeased with Vietnam's alliance with the Soviet Union. During its prolonged military occupation of Cambodia in 1979–89, Vietnam's international isolation extended to relations with the United States. The United States, in addition to citing Vietnam's minimal cooperation in accounting for Americans who were missing in action (MIAs) as an obstacle to normal relations, barred normal ties as long as Vietnamese troops occupied Cambodia. Washington also continued to enforce the trade embargo imposed on Hanoi at the conclusion of the war in 1975.