concessions were made on either side until U.S. President Jimmy Carter softened the American demand from a full accounting to simply the fullest possible accounting, and dispatched a diplomatic mission to Vietnam in 1977 to initiate normalization discussions. Although Vietnam was initially adamant about American economic assistance (their first postwar economic plan counted on the amount promised by President Nixon), the condition was dropped in mid-1978, when Vietnamese Foreign Minister Nguyễn Cơ Thạch and the U.S. government reached an agreement in principle on normalization, but the date was left vague. When Thạch urged November 1978, the U.S. government was noncommittal: at that time, the U.S. was preoccupied with a large influx in Vietnamese boat people, and they were already attempting to normalize relations with China; relations between Vietnam and China were strained at the time—eventually deteriorating into the Sino-Vietnamese War in 1979—and the U.S. did not wish to risk their relations with China by normalizing relations with one of China's enemies. The Vietnamese government responded by formalizing their relations with the Soviet Union. Their original hope, however, had been to gain both diplomatic recognition from the United States and a friendship treaty with the Soviet Union, as a double guarantee against future Chinese interference. In the U.S., the issue of normalizing relations with Vietnam was complicated by the Cambodian–Vietnamese War, the Vietnamese refugee crisis, and the unresolved POW and MIA issues, with U.S. President Ronald Reagan continuing to enforce the trade embargo and barring normalization as long as Vietnamese troops occupied Cambodia. Any efforts to improve relations remained closely tied to the U.S.' willingness to honor its 1973 aid commitment to Vietnam and Vietnam's failure to account for the whereabouts of American MIAs in Indochina. Beginning in mid-1978, however, Vietnam dropped its insistence that the MIA and aid questions be resolved as a precondition for normalization, and stopped linking the MIA issue to other unresolved matters between the two countries. Vietnamese leaders contrasted their restraint on the MIA issue with its alleged political exploitation by the United States as a condition for normal relations. As additional signs of goodwill, Hanoi permitted the joint U.S.-Vietnamese excavation of a B-52 crash site in 1985, and returned the remains of a number of American service members between 1985 and 1987. Vietnamese spokesmen also claimed during this period to have a two-year plan to resolve the MIA question, but did not reveal details. Although