structural:summarization
Retrocession and the Civil War

In the 1830s, the district's southern territory of Alexandria declined economically, due in part to its neglect by Congress. Alexandria was a major market in the domestic slave trade and pro-slavery residents feared that abolitionists in Congress would end slavery in the district. Alexandria's citizens petitioned Virginia to retake the land it had donated to form the district, a process known as retrocession.

The Virginia General Assembly voted in February 1846, to accept the return of Alexandria. On July 9, 1846, Congress went further, agreeing to return all territory that Virginia had ceded to the district during its formation. This left the district's area consisting only of the portion originally donated by Maryland. Confirming the fears of pro-slavery Alexandrians, the Compromise of 1850 outlawed the slave trade in the district, although not slavery itself.

The outbreak of the American Civil War in 1861 led to the expansion of the federal government and notable growth in the city's population, including a large influx of freed slaves. President Abraham Lincoln signed the Compensated Emancipation Act in 1862, which ended slavery in the district, freeing about 3,100 slaves in the district nine months before the Emancipation Proclamation. In 1868, Congress granted the district's African American male residents the right to vote in municipal elections.