They had three children: Alfred Slidell, Marie Rosine (later [on 30 Sept. 1872] comtesse [Countess] de St. Roman), and Marguerite Mathilde (later [on 3 Oct. 1864] baronne [Baroness] Frederic Emile d'Erlanger).

[4] Prior to the Mexican-American War, Slidell was sent to Mexico by President James Knox Polk to negotiate an agreement whereby the Rio Grande would be the southern border of Texas.

[5] Slidell warned Polk that the Mexican reluctance to negotiate a peaceful solution might require a show of military force by the United States to defend the border.

[6] Slidell was elected to the Senate in 1853 and cast his lot with other pro-Southern congressmen to repeal the Missouri Compromise, acquire Cuba, and admit Kansas as a slave state.

In the 1860 campaign, Slidell supported Democratic presidential candidate John C. Breckinridge but remained a pro-Union moderate until Abraham Lincoln's election resulted in the Southern states seceding.

After he was appointed the Confederate commissioner to France in September 1861, he ran the blockade from Charleston, South Carolina, with James Murray Mason of Virginia.

They then set sail from Havana on the British mail boat steamer RMS Trent but were intercepted by the US Navy while en route and taken into captivity at Fort Warren in Boston.

After some careful diplomatic exchanges, they admitted that the capture had been conducted contrary to maritime law and that private citizens could not be classified as "enemy despatches."