The Quasi-War was an undeclared war fought mostly at sea between the United States and the French Republic from 1798 to 1800 . In the United States , the conflict was sometimes also referred to as the Undeclared War With France , the Pirate Wars or the Half-War . The Kingdom of France had been a crucial ally of the United States in the American Revolutionary War from the spring of 1776 , and had signed in 1778 a Treaty of Alliance with the United States of America . But in 1794 , after the French Revolution toppled that country 's monarchy , the American government came to an agreement with the Kingdom of Great Britain , the Jay Treaty , that resolved several points of contention between the United States and Great Britain that had lingered since the end of the American Revolutionary War . It also contained economic clauses . The United States had already declared neutrality in the conflict between Great Britain and post-revolution France , and American legislation was being passed for a trade deal with Britain . Coupled with the U.S. refusal to continue repaying its debt to France on the grounds that the debt had been owed to the French Crown , not to Republican France , the French outrage at the United States led to a series of responses . The French privateers began seizing American ships trading with Britain and refused to receive the new United States minister Charles Cotesworth Pinckney when he arrived in Paris in December 1796 . In his annual message to Congress at the close of 1797 , President John Adams reported on France 's refusal to negotiate and spoke of the need `` to place our country in a suitable posture of defense '' . In April 1798 , President Adams informed Congress of the `` XYZ Affair '' , in which French agents had demanded a large bribe for the restoration of diplomatic relations with the United States . The French navy inflicted substantial losses on American shipping . Secretary of State Timothy Pickering reported to Congress on June 21 , 1797 , that the French had seized 316 American merchant ships in the previous eleven months . The hostilities caused insurance rates on American shipping to increase at least 500 percent , since French marauders cruised the length of the U.S. Atlantic seaboard virtually unopposed . The administration had no warships to combat them ; the last had been sold in 1785 . The United States possessed only a flotilla of small revenue cutters and some neglected coastal forts . Increased depredations by privateers from Revolutionary France required the rebirth of the United States Navy to protect the expanding American merchant shipping . Congress authorized the president to acquire , arm , and man not more than 12 vessels , of up to 22 guns each . Several vessels were immediately purchased and converted into ships of war , and construction of the frigate Congress resumed . July 7 , 1798 , the date that Congress rescinded treaties with France , is considered the beginning of the Quasi-War . This was followed two days later with the passage of the Congressional authorization to attack French warships . The U.S. Navy operated with a battle fleet of about 25 vessels . These patrolled the southern coast of the United States and throughout the Caribbean , seeking French privateers . Captain Thomas Truxtun 's insistence on the highest standards of crew training paid dividends as the frigate USS Constellation captured L'Insurgente and severely damaged La Vengeance . French privateers usually resisted , as did La Croyable , which was captured on July 7 , 1798 , by the USS Delaware outside of Egg Harbor , New Jersey . The USS Enterprise captured eight privateers and freed 11 American merchant ships from captivity . The USS Experiment captured the French privateers Deux Amis and Diane . Numerous American merchantmen were recaptured by the Experiment . The USS Boston forced Le Berceau into submission . Silas Talbot engineered an expedition to Puerto Plata harbor in the Colony of Santo Domingo , a possession of France 's ally Spain , on May 11 , 1800 ; sailors and marines from the USS Constitution under Lieutenant Isaac Hull captured the French privateer Sandwich in the harbor and spiked the guns of the Spanish fort . Only one U.S Navy vessel was captured by -- and later recaptured from -- French forces , the USS Retaliation . She was the captured privateer La Croyable , recently purchased by the U.S. Navy . Retaliation departed Norfolk on October 28 , 1798 , with Montezuma and Norfolk , and cruised in the West Indies protecting American commerce . On November 20 , 1798 , the French frigates L’Insurgente and Volontaire overtook Retaliation while her consorts were away and forced commanding officer Lieutenant William Bainbridge to surrender the out-gunned schooner . Montezuma and Norfolk escaped after Bainbridge convinced the senior French commander that those American warships were too powerful for his frigates and persuaded him to abandon the chase . Renamed Magicienne by the French , the schooner again came into American hands on June 28 , when a broadside from USS Merrimack forced her to haul down her colors . Revenue cutters in the service of the Revenue-Marine , the predecessor to the Coast Guard , also took part in the conflict . The cutter USRC Pickering , commanded by Edward Preble , made two cruises to the West Indies and captured several prizes . Preble turned command of the Pickering over to Benjamin Hillar , and she captured the much larger and more heavily armed French privateer l’Egypte Conquise after a nine-hour battle . In September 1800 , Hillar , the Pickering , and her entire crew were lost at sea in a storm . Preble commanded the frigate Essex , which he sailed around Cape Horn into the Pacific to protect American merchantmen in the East Indies ; he recaptured several ships that had been seized by French privateers . American naval losses may have been light , but the French successfully seized many American merchant ships by the war 's end in 1800 -- over two thousand , one source contends . Although they were fighting the same enemy , the Royal Navy and the United States Navy did not cooperate operationally , nor did they share operational plans or come to mutual understandings about deployment of their forces . The British did sell the American government naval stores and munitions . In addition , the two navies shared a system of signals by which each could recognize the other 's warships at sea , and allowed merchantmen of their respective nations to join each other 's convoys . By the autumn of 1800 , the United States Navy and the Royal Navy , combined with a more conciliatory diplomatic stance by the government of First Consul Napoleon Bonaparte , had reduced the activity of the French privateers and warships . The Convention of 1800 , signed on September 30 , ended the Franco-American War . Unfortunately for President Adams , the news did not arrive in time to help him secure a second term in the 1800 presidential election . The Quasi War has taken on a significant role in modern debates over the distribution of war powers between the Executive and Legislative branches in the US .