The territories of today´s USA and Mexico had been in constant contact since 1492, when Columbus officialy discovered America. In the 19th century, the USA purchased one part of the Mexican territory from its inhabitants after winning the war with Mexico.
As Mexicans were very experienced farmers, and the USA could not manage their own agriculture and industry, a particular need for Mexican farmers occurred. In the 20th century the very famous Bracero Program established US agriculture as the most advanced on Earth.