Immigrants are individuals who leave their country of origin to settle in another state. For the receiving state, this process is known as immigration, and for the sending state this phenomenon is emigration. For much of history, there were no restrictions on immigration. Thus, millions of Western European people migrated to the New World—now known as North and South America—as well as to areas of Africa and the South Pacific.

Unlike almost all other countries, the United States, Canada, and Australia continue to consider themselves to be "immigrant states," and to a large extent the data bear this out. From 1820 until the mid-1990s, over 60 million immigrants arrived on America's shores. In the decade of the 1990s, more than 10 million immigrants came to the United States. The immigration influence in Canada can be seen in the fact that immigrants presently make up...