Lyons–Seward Treaty (1862)
The United States and the United Kingdom agree in the Lyons–Seward Treaty to suppress the African slave trade.
Background
The United States had long resisted British efforts to suppress the Atlantic slave trade through mutual naval patrol agreements, particularly Britain's request for the right to search American vessels suspected of carrying enslaved people. Since the early 19th century, the US had refused to grant any foreign power the “right of search,” citing sovereignty and memories of British impressment before the War of 1812. Meanwhile, slave traders exploited American-flagged ships to evade capture, since other nations' navies dared not board them. The result was that the slave trade — abolished in the US in 1808 — continued to exploit this legal loophole for decades.
Did You Know?
Before the Lyons-Seward Treaty, American ships were effectively immune from search by the Royal Navy's Africa Squadron. Slave traders responded by flying the American flag to avoid capture — even if no American citizen was aboard. The treaty ended this practice by allowing each country's navy to board ships of the other suspected of carrying enslaved people.
The Treaty
Secretary of State William Seward negotiated the treaty with British minister Lord Lyons through the spring of 1862. The timing was significant: the US was in the midst of the Civil War, and the Lincoln administration was eager to demonstrate its moral commitment to antislavery principles — in part to discourage Britain from recognizing the Confederacy. On June 7, 1862, the Lyons-Seward Treaty was signed, granting each nation's navy the right to stop, board, and search the other's merchant vessels on the seas near Africa, Cuba, and the North American coast.
Aftermath & Legacy
The treaty had an almost immediate effect. Within two years, the Atlantic slave trade to Cuba — the last major destination for enslaved Africans — had virtually ended. The Royal Navy's West Africa Squadron and the US Navy were able to work together to intercept slave ships. The treaty marked a historic turning point: for the first time, the United States accepted international cooperation to enforce an antislavery policy, and it helped strengthen Anglo-American relations during the Civil War.