Union Captain Charles Wilkes the commander of the USS San Jacinto intercepted a British mail packet, the RMS Trent on November 8th 1861. The British ship was boarder and two Confederate diplomats; James Murray Mason and John Slidell, were found on board and removed under Union custody. The two men were on their way to England and France to try to get diplomatic recognition for the Confederacy and were traveling under the protection of the British flag.
The initial public reaction within the Union was to come together against Britain, but President Abraham Lincoln knew better then to risk a war on that front. The Confederate states thought this might be the thing that would hurt Federal and British relations and bring them recognition. In Britain there was outrage that their neutrality had been violated and they demanded an apology as well as the release of Mason and Slidell. There was even a movement of English troops to Canada for a possible invasion of Maine.
There were several weeks of tension which was resolved when Union Secretary of State William Seward made a disavowal of Captain Wilkes’ action saying he had erred in not bringing the RMS Trent in for adjudication violating the policy of freedom of the seas. There was no formal apology, but Mason and Slidell were released and allowed to continue on their diplomatic mission to Britain.