The present Mexican city was founded on April 13, 1823 on the north bank of the Pánuco River about from the Gulf, after Mexico achieved independence from Spain. Tampico built its economy on the exportation of silver; business development was mostly as a trading center and market town of an agricultural region. The town also became a common waypoint for the re-routing of African slaves to be illegally smuggled into the Southern United States, which had outlawed the international slave trade in 1807. In August 1829, Spain sent troops from Cuba to invade Tampico in an effort to regain control of the region, but in September, General Antonio López de Santa Anna forced the Spanish troops to surrender, and Mexican control of Tampico was reestablished.