Trent Affair, an incident during the American Civil War that almost brought war between the United States and Great Britain. On November 8, 1861, the British vessel Trent was boarded at sea by men from the American warship San Jacinto, commanded by Captain Charles Wilkes. Two Confederate agents who were passengers on the Trent were seized and taken into custody. James M. Mason, commissioner to Great Britain and France, and John Slidell, commissioner to France, were on their way to their posts to seek aid or intervention on behalf of the Confederacy. Wilkes had learned of their mission and took them prisoner without orders.

The commissioners' seizure was widely acclaimed in the North and in Congress, which gave Wilkes a medal. The British, however, were outraged. In a note that amounted to an ultimatum, even after being softened in wording by Prince Albert, the British government demanded their release. Lord Lyons, the British ambassador to the United States, delayed pressing the demand until public acclaim for Wilkes had died down.

Fearing possible war with Britain if the commissioners were not released, United States Secretary of State William H. Seward declared in December that Wilkes had acted without authority and had violated the principle of freedom of the seas. President Lincoln ordered the commissioners released, and they proceeded to Europe.