One important change that did make it into the final version included the agreement between northern and southern delegates to empower Congress to end the slave trade starting in 1808. Southern and northern delegates also agreed to strengthen the Fugitive Slave Clause in exchange for removing a requirement that two-thirds of Congress agree on "navigation acts" (regulations of commerce between states and foreign governments). The two-thirds requirement was favored by southern delegates, who thought Congress might pass navigation acts that would be economically harmful to slaveholders.