[2] At the outbreak of the American Civil War, Campbell opposed secession, and briefly served as a general in the Union Army.

[3] In 1835, Campbell moved back to Carthage, and was elected to Smith County's seat in the Tennessee House of Representatives.

[4] At the Battle of Monterrey later that year, this company lost one-third of its men in an assault on the town's citadel, earning the nickname, the "Bloody First.

Campbell on the other hand called the Compromise a "work of wisdom,"[5] and derided the Nashville Convention as treasonous.

[6] As governor, Campbell called for a more rational approach to resolving sectional strife, and demanded an end to the "insane" talk of secession.

[3] The Whigs nominated Gustavus A. Henry, who was defeated by the Democratic candidate Andrew Johnson in the general election.

In 1860, he supported Constitutional Union Party candidate and fellow Tennessee Whig John Bell for president.

[3] In early 1862, after the Union Army occupied Middle Tennessee, Assistant Secretary of War Thomas A. Scott recommended Campbell for military governor, but the appointment went to Andrew Johnson.

[5] On May 12, 1862, Campbell chaired a convention of Tennessee Unionists that mapped out a plan to bring the state back into the Union.

[1] Campbell defended Johnson during his impeachment hearings in the House in 1867, and served as an advisor during his trial in the Senate.

[11] Campbell's mother, Catherine Bowen, was a granddaughter of General William Russell (1735–1793), who had helped draft the Declaration of Independence.

[12] A house built by Campbell's uncle, John Henry Bowen (1770–1822), still stands in Gallatin, and is listed on the National Register as the Trousdale Place.

After his uncle's death, the house was, ironically, purchased by William Trousdale, Campbell's future gubernatorial opponent.