From 1910 to 1929, one-tenth of Mexico’s population (about one million people) moved to the United States. This historic wave of migration came to a halt in the 1930s, and in the new decade, more Mexicans left the U.S. than entered. In this lesson, students examine congressional testimony, photographs, industry correspondence, and state legislation to answer the question: Why did Mexican migration to the U.S. drastically change in the 1930s?