On November 8, 1861, USS San Jacinto, commanded by Union Captain Charles Wilkes, intercepted the British mail packet RMS Trent and removed, as contraband of war, two Confederate envoys: James Murray Mason and John Slidell. The envoys were bound for Britain and France to press the Confederacy's case for diplomatic recognition and to lobby for possible financial and military support.

Public reaction in the United States was to celebrate the capture and rally against Britain, threatening war. In the Confederate states, the hope was that the incident would lead to a permanent rupture in Anglo-American relations and possibly even war, or at least diplomatic recognition by Britain. Confederates realized their independence potentially depended on intervention by Britain and France. In Britain, there was widespread disapproval of this violation of neutral rights and insult to their national honor. The British government demanded an apology and the release of the prisoners and took steps to strengthen its military forces in British North America and the North Atlantic.

President Abraham Lincoln and his top advisors did not want to risk war with Britain over this issue. After several tense weeks, the crisis was resolved when the Lincoln administration released the envoys and disavowed Captain Wilkes's actions, although without a formal apology. Mason and Slidell resumed their voyage to Europe.