More than any other Factor, The Iranian Revolution of 1978–79 and its aftermath have contributed to the growth of the Iranian diaspora population worldwide. The revolution precipitated the exodus of Iranian exiles or political refugees, and the establishment of the Islamic Republic of Iran further discouraged the return of many Iranians already abroad. As a result, by about 1990, 637,500 Iranians were enumerated in official national censuses of the following ten countries on four continents: U.S., Canada, West Germany, Sweden, Great Britain, France, Norway, Australia, Israel, and Japan.
With an Iranian population—defined as persons either born in Iran or of Iranian ancestry—of 285,000 in 1990, the U.S. contained nearly half (45%) of the Iranians living in the above-mentioned Western and Asian countries. This overwhelming concentration, an availability of good data on immigrants (including Iranians), and a number of Iranian students who have become social scientists in the U.S., have encouraged research on this group.