[1][2][3] In July 1861, Buchanan enlisted for the American Civil War as a private in the Confederate States Army's Company D, 4th Virginia Infantry Regiment, Stonewall Brigade.

[4][5] He took part in several engagements, and was detailed to several additional duties, including military hospital nurse for six months in 1862, and teamster in May and June 1863.

[2][3][10] Among Buchanan's civic activities was membership in Abingdon's Maury Literary Association, including a term as first vice president.

[a][13] A Democrat in politics, Buchanan was a delegate to numerous local and state party conventions, and routinely gave speeches at rallies and other campaign events.

[14][15][16] During the post-Reconstruction era in Virginia, politics was dominated by the issue of "readjustment" ‒ whether the state would honor its pre-Civil War and wartime debts, including bond issues that financed infrastructure projects, or whether the debt would be "readjusted" to a lower amount through refinancing some obligations at lower interest rates, repudiating others, and other similar measures.

[17] Buchanan was identified with the Conservative Party, which worked throughout the 1870s and early 1880s to defeat Republicans and Readjusters and "redeem" Virginia.