"When the agreement between the United States, Mexico and Canada went into effect in 1994, it removed nearly all trade barriers between the countries. Among the industries affected was agriculture, forcing small Mexican farmers into direct competition with big American agribusiness. Cheap American corn – heavily subsidized, mechanized and genetically modified – soon flooded the Mexican market to the detriment of local farmers. As U.S. farmers exported their subsidized corn to Mexico, local producer prices plummeted and small farmers could no longer earn enough to live on."
Via Seth Dixon