On October 1, 1949, Mao Zedong declared the creation of the People’s Republic of China (PRC) with the takeover by the communists. This led to the US suspending diplomatic ties with the PRC until January 1, 1979. This and China’s subsequent entry into the Korean War led to the racist purge that sent leading Chinese scientists back to China including six of the top fifteen who worked on China’s bomb (Zhao Zhongyao was one of Qian’s colleagues at Caltech) and four of the top five in the missile development including Qian.
At the time of the Korean War, there were 1,600 Chinese students enrolled in 454 colleges and universities and another thousand not enrolled but working on theses or undergoing special technical or professional training according to the Institute of International Education News Bulletin in March 1956. They constituted the largest contingent after Canadians. Almost half the Chinese students were in studies related to nuclear development. They were the best of the Chinese scientific braintrust and mostly came from bourgeois families. Their source of funding stopped with the communist takeover. Most of them did not want to return to China and a later survey found that the prime motivating factor was their treatment by the Immigration Service.
In 2018-19 Chinese students in the US numbered almost 370,000. They accounted for almost 44% of international students and were the largest group from any country.