Immigration, process through which individuals become permanent residents or citizens of another country. Historically, the process of immigration has been of great social, economic, and cultural benefit to states. The immigration experience is long and varied and has in many cases resulted in the development of multicultural societies; many modern states are characterized by a wide variety of cultures and ethnicities that have derived from previous periods of immigration. In the post-World War II period, immigration was largely the result of the refugee movement following that war and, during the 1950s and ’60s, the end of colonization across Asia and Africa. Immigration from these areas to former imperial centres, such as the United Kingdom and France, increased. In the United Kingdom, for example, the 1948 British Nationality Act gave citizens in the former colonial territories of the Commonwealth (a potential figure of 800 million) the right of British nationality.