[macintux]

> Anyway, for whatever reasons I forget now, DC decided in the 1800s to give the VA side back to the state of VA.

As seems to be the dominant theme of the 1800s in the U.S, the answer is slavery. Thanks, I hadn’t heard about this.

> In the 1830s, the district's southern territory of Alexandria went into economic decline partly due to neglect by Congress. The city of 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, further depressing the local economy. Alexandria's citizens petitioned Virginia to take back the land it had donated to form the district, through a process known as retrocession.

> The Virginia General Assembly voted in February 1846 to accept the return of Alexandria. On July 9, 1846, Congress agreed to return all the territory that Virginia had ceded. Therefore, the district's area consists 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.

https://en.wikipedia.org/wiki/Washington,_D.C.#Retrocession_...