Although growth of the urban labor force exceeded even the growth rate of industrial employment, with surplus workers taking low-paying service jobs, many Mexican laborers migrated to the United States where wages were higher. During World War II, Mexico–United States relations had improved significantly from the previous three decades. The Bracero Program was set up with orderly migration flows were regulated by both governments. However. many Mexicans could not qualify for the program and migrated north illegally, without permission from their own government and without sanction from the U.S. authorities. In the post-war period as the U.S. economy boomed and as Mexico's entered a phase of rapid industrialization, the U.S. and Mexico cooperated closely on illegal border crossings by Mexicans. For the Mexican government, this loss of labor was "a shameful exposure of the failure of the Mexican Revolution to provide economic well-being for many of Mexico's citizens, but it also drained the country of one of its greatest natural resources, a cheap and flexible labor supply." The U.S. and Mexico cooperated closely to stop the flow, including the 1954 program called Operation Wetback.