The Trent Affair was a diplomatic incident in 1861 during the American Civil War that threatened a war between the United States and the United Kingdom. The U.S. Navy captured two Confederate envoys from a British Royal Mail steamer; the British government protested vigorously. American public and elite opinion strongly supported the seizure, but it worsened the economy and was ruining relations with the world's strongest economy and strongest navy. President Abraham Lincoln ended the crisis by releasing the envoys.

On November 8, 1861, , commanded by Union Captain Charles Wilkes, intercepted the British mail packet and removed, as contraband of war, two Confederate envoys: James Murray Mason from Virginia and John Slidell from Louisiana. 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 cause 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 honour. The British government demanded an apology and the release of the prisoners and took steps to strengthen its military forces in British North America (Canada) 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.

Background Relations with the United States were often strained and even verged on war when Britain came near to supporting the Confederacy in the early part of the American Civil War. British leaders were constantly annoyed from the 1840s to the 1860s by what they saw as Washington's pandering to the mob, as in the Oregon boundary dispute of 1844 to 1846. These tensions came to a head during the Trent affair; this time London would draw the line.George L. Bernstein, "Special Relationship and Appeasement: Liberal policy towards America in the age of Palmerston." Historical Journal 41 #3 (1998): 725–750.

The Confederacy and its president, Jefferson Davis, believed from the beginning that European dependence on Southern cotton for its textile industry would lead to diplomatic recognition and intervention, in the form of mediation. Historian Charles Hubbard wrote:

The Union's main focus in foreign affairs was just the opposite: to prevent any British recognition of the Confederacy. The issues of the Oregon boundary dispute, British involvement in Texas, and the Canada–US border dispute had all been resolved in the 1840s, and despite the Pig War of 1859, a minor border incident in the Pacific Northwest, Anglo-American relations had steadily improved throughout the 1850s. Secretary of State William H. Seward, the primary architect of American foreign policy during the war, intended to maintain the policy principles that had served the country well since the American Revolution: non-intervention by the United States in the affairs of other countries and resistance to foreign intervention in the affairs of the United States and other countries in the Western Hemisphere.Jones, pp. 2–3; Hubbard, p. 17; Mahin, p. 12.

British prime minister Lord Palmerston urged a policy of neutrality. His international concerns were centered in Europe, where both Napoleon III's ambitions in Europe and Bismarck's rise in Prussia were occurring. During the Civil War, British reactions to American events were shaped by past British policies and their own national interests, both strategically and economically. In the Western Hemisphere, as relations with the United States improved, Britain had become cautious about confronting the United States over issues in Central America.

As a naval power, Britain had a long record of insisting that neutral nations honor its blockades of hostile countries. From the earliest days of the war, that perspective would guide the British away from taking any action that might have been viewed in Washington as a direct challenge to the Union blockade. From the perspective of the South, British policy amounted to de facto support for the Union blockade and caused great frustration.Berwanger, p. 874; Hubbard, p. 18; Baxter, The British Government and Neutral Rights, p. 9. Baxter wrote that "the British government, while defending the rights of British merchants and shipowners, kept one eye on the precedents and the other on the future interests of the mistress of the sea."

The Russian Minister in Washington, Eduard de Stoeckl, noted, "The Cabinet of London is watching attentively the internal dissensions of the Union and awaits the result with an impatience which it has difficulty in disguising." De Stoeckl advised his government that Britain would recognize the Confederate States at its earliest opportunity. Cassius Clay, the US minister in Russia, stated, "I saw at a glance where the feeling of England was. They hoped for our ruin! They are jealous of our power. They care neither for the South nor the North. They hate both."Graebner, pp. 60–61.

At the beginning of the Civil War, the U.S. minister to the Court of St. James was Charles Francis Adams. He made clear that Washington considered the war strictly an internal insurrection affording the Confederacy no rights under international law. Any movement by Britain towards officially recognizing the Confederacy would be considered an unfriendly act towards the United States. Seward's instructions to Adams included the suggestion that it be made clear to Britain that a nation with widely scattered possessions, as well as a homeland that included Scotland and Ireland, should be very wary of "set[ting] a dangerous precedent".Mahin, p. 47; Taylor, p. 177.

Lord Lyons, an experienced diplomat, was the British minister to the US. He warned London about Seward:

Despite his distrust of Seward, Lyons, throughout 1861, maintained a "calm and measured" diplomacy that contributed to a peaceful resolution to the Trent crisis.Dubrulle, p. 1234.

Issue of diplomatic recognition (February–August 1861)

The Trent affair did not erupt as a major crisis until late November 1861. The first link in the chain of events occurred in February 1861, when the Confederacy created a three-person European delegation consisting of William Lowndes Yancey, Pierre Rost, and Ambrose Dudley Mann. Their instructions from Confederate Secretary of State Robert Toombs were to explain to these governments the nature and purposes of the southern cause, to open diplomatic relations, and to "negotiate treaties of friendship, commerce, and navigation". Toombs' instructions included a long legal argument on states' rights and the right of secession. Because of the reliance on the double attack of cotton and legality, many important issues were absent from the instructions including the blockade of Southern ports, privateering, trade with the North, slavery, and the informal blockade the Southerners had imposed whereby no cotton was being shipped out.Donald, Baker, Holt, pp. 311–312; Hubbard, pp. 27–29.

British leaders—and those on the Continent—generally believed that division of the U.S. was inevitable. Remembering their own unsuccessful attempt to keep their former American colonies in the Empire by force of arms, the British considered Union efforts to resist a fait accompli to be unreasonable, but they also viewed Union resistance as a fact that they had to deal with. Believing the war's outcome to be predetermined, the British saw any action they could take to encourage the end of the war as a humanitarian gesture. Lyons was instructed by Foreign Secretary Lord Russell to use his own office and any other parties who might promote a settlement of the war.Jones, pp. 3–4, 35.

The commissioners met informally with Russell on May 3. Although word of Fort Sumter had just reached London, the immediate implications of open warfare were not discussed at the meeting. Instead the envoys emphasized the peaceful intent of their new nation and the legality of secession as a remedy to Northern violations of states' rights. They closed with their strongest argument: the importance of cotton to Europe. Slavery was discussed only when Russell asked Yancey whether the international slave trade would be reopened by the ConfederacyThe Constitution of the Confederate States, drafted in March 1861, included an explicit prohibition on the importation of slaves from any source except the United States, but it was not ratified until February 1862. (a position Yancey had advocated in recent years); Yancey's reply was that this was not part of the Confederacy's agenda. Russell was noncommittal, promising the matters raised would be discussed with the full Cabinet.Hubbard, pp. 34–39; Walther, p. 308. Russell had written to Lyons about the arrival of the three Confederates: "If it can possibly be helped, Mr. Seward must not be allowed to get us into a quarrel. I shall see the southerners when they come, but unofficially, and keep them at a proper distance." Graebner, p. 64.

In the meantime, the British were attempting to determine what official stance they should have to the war. On May 13, 1861, on the recommendation of Russell, Queen Victoria issued a declaration of neutrality that served as recognition of Southern belligerency—a status that provided Confederate ships the same privileges in foreign ports that U.S. ships received. Confederate ships could obtain fuel, supplies and repairs in neutral ports but could not secure military equipment or arms. The availability of Britain's far-flung colonial ports made it possible for Confederate ships to pursue Union shipping throughout much of the world. France, Spain, the Netherlands, and Brazil followed suit. Belligerency also gave the Confederate government the opportunity to purchase supplies, contract with British companies, and purchase a navy to search out and seize Union ships. The Queen's proclamation made clear that Britons were prohibited from joining the military of either side, equipping any ships for military use in the war, breaking any proper blockade, and transporting military goods, documents, or personnel to either side.Mahin, p. 48; Graebner, p. 63; Donald, Baker, Holt, p. 312.

On May 18, Adams met with Russell to protest the declaration of neutrality. Adams argued that Great Britain had recognized a state of belligerency "before they [the Confederacy] had ever showed their capacity to maintain any kind of warfare whatever, except within one of their own harbors under every possible advantage […] it considered them a maritime power before they had ever exhibited a single privateer upon the ocean." The major United States concern at this point was that the recognition of belligerency was the first step towards diplomatic recognition. While Russell indicated that recognition was not currently being considered, he would not rule it out in the future, although he did agree to notify Adams if the government's position changed.Mahin, pp. 48–49; Hubbard, p. 39; Jones, p. 34.