Ethnic Chinese immigration to the United States since 1965 has been aided by the fact that the United States maintains separate quotas for Mainland China, Taiwan, and Hong Kong. During the late 1960s and early and mid-1970, Chinese immigration into the United States came almost exclusively from Hong Kong and Taiwan creating the Hong Kong American and Taiwanese American subgroups. Immigration from Mainland China was almost non-existent until 1977, when the PRC removed restrictions on emigration leading to immigration of college students and professionals. These recent groups of Chinese tended to cluster in suburban areas and to avoid urban Chinatowns.