The District of Columbia Organic Act of 1801 created two counties with the District of Columbia: Washington County on the east side of the Potomac River and Alexandria County on the west side. A variety of poltical maneuvering led to retrocession of Alexandria County back to Virginia in 1846. After the Civil War, Virginia adopted the Underwood Constitution of 1869, which created magisterial districts within each county. Alexandria County had three districts: Washington District was roughly the area north of I-66; Jefferson District was roughly the area south of Arlington Cemetary and I-395; and Arlington District was in the center of the county.
The new Virginia constitution also allowed cities over 10,000 people to cede from the county and become independent. Alexandria City promptly took advantage of this clause and ceded from Alexandria County in 1870, taking away the southern tip of Jefferson District. The subsequent tension and confusion between Alexandria City and Alexandria County led to the latter changing its name to Arlington County in 1920.
In the late 1890s, Jefferson District began filling in with suburbs of Alexandria, such as Del Ray and St. Elmo (which became the Town of Potomac), Rosemont, Braddock Heights, Mt. Ida, George Washington Park and North Alexandria. As most of the population in these suburbs worked in or had other ties to Alexandria City, the city began annexing these areas in the early 20th Century. In 1915, the first annexation trimmed more off the southern end of Jefferson District, absorbing Rosemont and parts of Braddock Heights by pushing the western boundry of the city from West Street out to the foot of Ivy Hill. During the 1920s, Alexandria successfully lobbied to extend its northern border, and on January 1st, 1930, the area of Jefferson District south of Four Mile Run was also annexed into the City of Alexandria.
Arlington County leaders fought to avoid this annexation. Among other efforts, they successfully pursued an amendment to the Virginia Constitution in 1928, which allowed alternative forms of county government. Once this amendement was passed, they sought legislature which allowed Arlington to assume a County Manager form of government, much like a city government. Arlington County adopted this form of government in 1932, abolishing the magisterial districts within the county. Although too late to stave off the annexation of most of Jefferson District, the new form of government effectively blocked further annexation by eliminating the ability of a magisterial district to vote independently of the rest of the county. Arlignton County officials publicly touted this change as a means to "safeguard Arlington County from further annexation by the City of Alexandria."