Final answer:
The answer is false. China's main adversary by the end of the 1960s was not the U.S. but rather the Soviet Union, as tensions between the two communist powers escalated, culminating in border conflicts. U.S. recognition of this rift culminated with President Nixon's visit to China in 1972.
Step-by-step explanation:
By the end of the 1960s, the statement that China continued to regard the U.S. as its main adversary is false. During this period, the relationship between China and the Soviet Union significantly deteriorated, leading to heightened tensions between the two communist powers. The Sino-Soviet split became increasingly evident, and after the border clashes in 1969, the possibility of a military conflict between China and the Soviet Union seemed likely. Consequently, China's focus on the U.S. as a principal adversary diminished as it faced a more pressing threat from its communist neighbor. This situation was underscored by a lack of substantial aid from Communist nations to North Vietnam, contrasting with the significant assistance from the U.S. to South Vietnam.
Additionally, the U.S. foreign policy was still presenting international Communism as a united front, despite the growing rift between China and the Soviet Union. Only with President Nixon's visit to China in 1972 did a thaw in relations between China and the U.S. begin, marking a shift in international dynamics and indicating the decreasing view of the U.S. as China's primary adversary.