The correct answer here is agriculture.
Agriculture is the cultivation of plants and breeding of animals in order to provide food and other products to sustain life. Agriculture created food surpluses which was the main reason for people to be able to live in cities. The major agricultural products are : food, fibers, fuels, raw materials ( rubber ). Over one third of the world's workers are employed in agriculture.
The United States leads worldwide in cotton exportation ( behind China and India). Almost all of the cotton fiber growth and production occurs in southern and western states such as : Texas, California, Arizona, Mississippi, Arkansas and Louisiana. Over the centuries, cotton became a staple crop in American agriculture.