On this day in 1861, the United States found itself in a contretemps with Britain that almost ended in a war the country could ill afford, given that it was at war with its own Southern states at the time. It started with a Navy captain going rogue.
Two Confederate diplomants, James M. Mason and John Slidell, were headed to Europe on the British mail steamer Trent to drum up foreign support for the war. A captain of the newly formed U.S. Navy, Charles Wilkes, “commanded the crew of the U.S.S. San Jacinto to intercept the ... Trent and arrest ... James M. Mason and John Slidell,” writes the Library of Congress. They were “brought ashore and imprisoned at Fort Warren in Boston Harbor,” the library writes.
The problem was that Britain was a neutral party in the war. That meant that when United States officers boarded the ship, it counted as an act of aggression towards a neutral party.
“Despite initial rejoicing by the Northern populace and Congress, this unauthorized seizure aroused a storm of indignant protest and demands for war throughout Britain,” writes Encyclopedia Britannica. “The British government sent an ultimatum demanding an American apology and the release of Mason and Slidell.”
For a bit, it actually seemed like Britain and the United States might go to war. “While the British were furious at this violation of the British flag and demanded their release, Americans seemed to relish the possibility of imminent war,” writes historian George M. Blackburn. The British started building up their military forces in the States in anticipation of a conflict.
“Ultimately, however, Washington officials realized that retaining the Confederates might well lead to war with Britain and thus make the Confederate mission a resounding success; besides, the British had international law on their side.”
They returned Mason and Slidell, who did go on to England, he writes. Secretary of State William H. Seward apologized in the interests of avoiding conflict, writes the Library of Congress. Thanks to this diplomacy, the incident turned out to be surprisingly anticlimatic despite weeks of drama.
The incident had never been part of the United States's plan: Wilkes had gone off-book when boarding the Trent. In the interests of avoiding a major international incident, Abraham Lincoln was forced to disavow his actions. Wilkes' talent for acting out led to other incidents that eventually ended his career, writes Encyclopedia Britannica.
The Trent affair was “the first major diplomatic controversy of the Civil War,” writes Blackburn. In England and France, it helped to spark a major debate over whether both the United States and the Confederacy should be diplomatically recognized on the same footing. They weren't, and Britain eventually supported the United States against the Confederacy, but in the meantime, tensions ran high.