Final answer:
During World War II, the bracero program brought thousands of impoverished Mexicans to the United States to work in agriculture, primarily in California.
Step-by-step explanation:
The bracero program, which was instituted on August 4, 1942, brought thousands of impoverished Mexicans into the United States to work as braceros, or manual laborers, primarily in agriculture. This program aimed to address the labor shortage in California fields during World War II. The migration of Mexican agricultural workers to California in particular increased during this time, as it provided employment opportunities in the agricultural sector.