Why did Jefferson use the U.S. navy against North African states? - The Barbary pirates held American merchant ships hostage and Jefferson sent in the navy rather than pay the ransom. - Jefferson wanted to disarm the pasha of Tripoli, who had gathered weapons he planned to use against the United States. - Plantation owners wanted to import more Africans before the international slave trade became illegal in 1808, and they needed American firepower to help them do it.