The ancestors of the American Indians are thought to have come to the North American continent over a land bridge from Asia some time in the remote past. All other Americans trace their ancestry to relatively recent migrants. From the time of the Pilgrims, some 32 million immigrants, mostly from Europe, settled in the united States intolerant political states, mostly but not exclusively communist, ha e made life in their native lands intolerable for many people. Millions of refugees fled persecution and possible death during and immediately after World War II, and oppression since has sent millions fleemg from Cuba, Uganda, Palestine, Hungary, Czechoslovakia, ‘ietnam,Cambodia, Nicaragua, El Salvador, and Laos. Many of them have found new homes in theUnited States and elsewhere, but in 1982 there were still 10 million pole living i c dle, over 8 million of whom live in developing countrie [U,S. Committ for Refugees, World 1 , 1 82, . 40]. The pull factor ref rs to the attractions in the receiving country, such as economic opportunity, climate, and type of government. ‘Ihis often means that many immigrants go to states already he populated like California, while few go to remote and spar e y peopled but less a t places such as Alaska. Channels refer to the means of movement from one place to another and the
presence or absence of barrier . In this respect, transportation has never been easier , but legal barriers such as emigration prohibitions and immigration restrictions have never been more formidable.