A flow of Mexican migration to the US started little after the establishment of the 1847 border, which is still in place today. Since then, migration has progressed parallel to the socioeconomic and political processes in both countries. At the end of the 19th century, Americans started recruiting Mexican labor to build railroads and to work the booming industries of Chicago. In the early 1900s, 17% of the most important railroad’s workers were Mexican. A few years later, many Mexicans fled the Mexican Revolution (1910-1920) and poured into the US, Cuba and Guatemala. When World War I broke out, the demand for agricultural labor rose— this is why so many Mexicans came to work in the rural sectors of the US. A huge turnaround occured in the 1930s during the Great Depression: the US sent 347,000 Mexicans back south of the border. Nevertheless, during World War II, the demand for laborers shot up again and a bilateral “arms” agreement allowed 4.6 million Mexicans to temporarily work the fields again. Most of these workers came from rural and uneducated sectors of the population. More recently, the economic crisis triggered by a huge oil bust in the 1980s caused many Mexicans to migrate to the US in search of jobs. Along with the previous process of labor demand and expulsion, there have been migration laws shaping the population shifts of the US. The 1965 Law eliminated discrimination in the visa-granting process. This law was really intended to promote European immigration, but it actually encouraged immigration from Latin America, the Caribbean and Asia. The Immigration Reform and Control Act-IRCA-1986 conceded visas to undocumented workers, and allowed women and children to join the male immigrants in the US. During the 1990s and 2000s, the migratory influx of Mexicans has stayed high, despite tighter restrictions at the border