 The great majority of Mexican emigrants have moved to the United States of America.This migration phenomenon is not new, but it has been a defining feature in the relationship of both countries for most of the twentieth century.During World Wars I and II, the United States government approved the recruitment of Mexican workers in their territory, and tolerated unauthorized migration in order to obtain additional farm- and industrial-workers to fill the necessary spots vacated by the population in war, and to supply the increase in the demand for labor.