Thomas Jefferson believed that the independent, self-sufficient farmer was the foundation of democracy. At the time of his presidency, agriculture provided 75% of exports. To support farming, the federal government advanced white male ownership of farmland through a variety of measures, including the Northwest Ordinance in 1787, the Louisiana Purchase in 1803, and the Homestead Act of 1862.
Yet, agricultural practice also included millions of slaves whose labor became the basis of planter prosperity. After the Civil War, most of their freed descendants, along with many whites, became sharecroppers and tenant farmers saddled with heavy debt and abusive landlords, oppressed by a harsh social, economic and political system. Farmers who owned their own land were also often subject to heavy debt, high interest rates, and inflated shipping costs from railroads, as well as fluctuating prices in the commodity markets, and the vagaries of droughts and floods. Such conditions gave rise to a variety of protest movements and organizations, such as the Populist Party and the Southern Tenant Farmers Union from the late 19th century through the New Deal.
In the early 20th century, agriculture still dominated the U.S. economy, but large growers and corporations increasingly came to rule farming, often relying on low-wage migrant workers for their labor. For decades, migrants have come to California and the American West to harvest crops. During the Great Depression, after the Dust Bowl destroyed their farms in the southern Plains, Okies traveled west to start again. Growers today in California and the Southwest rely heavily on often exploited Mexican and Mexican-American laborers to work the fields.
The United States remains one of the most productive agricultural economies in the world. Even as the percentage of people employed in agriculture has declined from 41% in 1900 to 1.9% in 2000, U.S. farms have been able to produce more food than ever before through mechanization and advanced animal and plant breeding. The use of fertilizers and pesticides and the creation of genetically modified foods have also increased productivity, but are controversial. Health concerns about harmful pesticides have led many farmers and consumers to organic foods.