 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 . 
