Slavery began in the English colony of Jamestown in 1619. It started with the purchase of 20 Africans—not as reported by John Rolfe from a Dutch ship—but rather from an English warship named the "White Lyon." The Colonists in the Virginia Colony bought the contracts of the Africans as indentured servants. Not long after this it became a custom to hold slaves for life in the colonies. During the 17th and 18th centuries, slaves were used to raise crops of tobacco and food crops. After the invention of the cotton gin in 1793, cotton became the most important crop. At this point slavery became a critical part of the South's economy. With westward expansion, the question of slavery in the new territories became a subject of great debate. It polarized the nation between the interests of the Northern industrial economy and the South's agricultural economy.