lexandria's population numbered 4,200 in 1800, and the city prospered by trading the agricultural products of the Virginia Piedmont in world markets, especially New England, Spain, and Portugal. Civic amenities arose, and the quality of life improved, but the city also suffered from periodic epidemics typical of ports and occasional fires that ravaged the commercial district.

During the War of 1812, the city faced disaster when the British fleet sailed up the Potomac to capture Washington in 1814. Defenseless, Alexandria surrendered and suffered from five days of looting by the British and scorn from fellow Americans, but the enemy did not burn the wharves and warehouses. Trade fell off after the war, and the city did not recover from the Panic of 1819 for a generation. In 1843, just as the canal connecting to the Chesapeake and Ohio Canal was completed, the new technology of railroads superseded it, carrying western trade to Baltimore instead of Alexandria.

As a federal city, Alexandria offered opportunities for free blacks not found elsewhere in Virginia, but the port also became a center of the domestic slave trade. Fear that the slave trade would be abolished in the District of Columbia (which occurred in 1850) contributed to disenchantment with the city's status. Combined with regulations banning national public facilities south of the Potomac, and limits on banking, Alexandrians clamored to return to Virginia. Congress passed an act to cede the Virginia portion of the District back to Virginia, the voters passed it (in Alexandria by 763 to 222) , and on March 13, 1847, the city reverted to Virginia.