Mexican migration to the United States: defacto rules

"Migration from Mexico to the United States is viewed very differently by those two nations. The United States perspective is that of illegal immigrants invading their nation, especially during times of national unemployment. From the Mexican perspective, people migrate across the border in response to quite predictable labor supply and demand pressures. The fact that for many years the United States held undocumented labor to be punishable for the worker but not for the employer suggests a tacit recognition of the labor supply/demand factor, but a recognition tainted by discrimination."