First Barbary War, also called Tripolitan War, (1801–05), conflict between the United States and Tripoli (now in Libya), incited by American refusal to continue payment of tribute to the piratical rulers of the North African Barbary States of Algiers, Tunis, Morocco, and Tripoli. This practice had been customary among European nations and the nascent United States in exchange for immunity from attack on merchant vessels in the Mediterranean.

Tripolitan War; Philadelphia The U.S. frigate Philadelphia being seized by Tripolitan gunboats in Tripoli's harbour during the Tripolitan War, undated engraving. Library of Congress, Washington, D.C.

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A demand from the pasha of Tripoli for greater tribute and his dramatic declaration of war on the United States (May 14, 1801) coincided with a decision by U.S. Pres. Thomas Jefferson’s administration to demonstrate American resolve. Despite his opposition to the expense of maintaining a navy, Jefferson dispatched an American naval squadron to Tripolitan waters. By means of a special “Mediterranean Fund,” the navy—which had been partially dismantled and was perhaps nearing extinction—actually increased in size.

During the following years, American warships fought in the waters around Tripoli, and, in 1803, when Commodore Edward Preble became commander of the Mediterranean squadron, greater successes ensued. The intrepid Preble sailed into Tangiers to rescue a number of American prisoners, and, on February 16, 1804, he ordered his young lieutenant, Stephen Decatur, to undertake the spectacular raid in which the captured U.S. frigate Philadelphia was destroyed in the harbour of Tripoli.

The combination of a strong American naval blockade and an overland expedition from Egypt finally brought the war to a close, with a treaty of peace (June 4, 1805) favourable to the United States. The other Barbary rulers, though considerably chastened, continued to receive some tribute until 1816.