"Migration from Mexico and Central America?s ?Northern Triangle? region (El Salvador, Guatemala, and Honduras) to the United States has increased significantly in the past four decades, from less than 1 million immigrants in the 1970s to 14 million today. Propelled by difficult economic and social conditions at home, massive opportunity differentials, and strengthening social networks, these regional migration flows have been shaped by evolving policies and practices. This report examines the push-and-pull factors of migration in the region from three major migration periods: the mostly laissez faire policies prior to the 1930s, the large-scale Bracero temporary worker program before and after World War II, and the mostly illegal system that emerged after the Bracero Program?s end in 1964." MPI, Aug. 2011.