His ranch adjoined the Rio Grande, the river that formed the boundary between the United States and Mexico, with its poverty, caste system, and systemic corruption. So the poor Mexicans migrated. Over thirteen million of them, over a fifth of the Mexican population, had crossed that border illegally in the last fifty years and were grubbing for work in the United States, usually for minimum wage, or living on welfare and food stamps. Illiterate, unskilled, and usually unable to speak English, they flooded the schools with their children, kept blue-collar wages low, and formed an underclass that resisted assimilation and required huge amounts of public assistance dollars.