[failed verification][4] Brent took part in a "Convention of the Delegates from the Southern Counties, in favor of a Division of the State" and was appointed to a committee to draft a concluding resolution, along with Benjamin Hayes, J.S.K.

[9] In mid-February 1861, Joseph Lancaster Brent, as a wealthy attorney and former state legislator of southern sympathies, was one of the prominent Angelenos who signed the petition to form the Los Angeles Mounted Rifles in response to a call by Governor John G. Downey for the formation of militia companies "to preserve order" just before the start of the American Civil War.

Brent decided to return to the east, sold his rancho, and boarded the Panama steamer SS Orizaba at San Diego.

Senator William M. Gwin and former U.S. Attorney Calhoun Benham, also trying to make it back to join the South's war effort.

They were, however, arrested in Panama City on a charge of treason, by Brigadier General Edwin Vose Sumner while in Colombian waters.

This incident could have involved the United States in a war with Colombia except for the trio giving consent to the arrest in order to avoid any harm to the citizens of Panama City.

General Taylor ordered Brent to engage the Union ironclad with two boats, the former tugboat Webb and recently captured paddle steamer Queen of the West.

They overtook Indianola and attacked from each side, ramming her seven times before the ironclad ran her bow on the west bank of the river and surrendered.

It ended Admiral David Dixon Porter's efforts to blockade the Red River by detached vessels while keeping the body of his fleet above Vicksburg, Mississippi, and it prompted Farragut's costly run by the South's forts at Port Hudson, March 14, 1863.