It might sound like something out of “Sesame Street” but the XYZ Affair was, in fact, a diplomatic incident between France and America in the late 18th century that led to an undeclared war at sea.

In 1793, France went to war with Great Britain while America remained neutral. Late the following year, the United States and Britain signed the Jay's Treaty, which resolved several longstanding issues between those two nations. The French were infuriated by Jay’s Treaty, believing it violated earlier treaties between the United States and France; as a result, they went on to seize a substantial number of American merchant ships.

When President George Washington sent Charles Cotesworth Pinckney as the U.S. minister to France in 1796, the government there refused to receive him. After John Adams became president in March 1797, he dispatched a three-member delegation to Paris later that same year in an effort to restore peace between the two countries. Once the diplomats—Pinckney along with John Marshall and Elbridge Gerry—arrived overseas they tried to meet with France’s foreign minister, Charles de Talleyrand. Instead, he put them off and eventually had three agents inform the U.S. commissioners that in order to see him they first would have to pay him a hefty bribe and provide France with a large loan, among other conditions.

Pinckney’s supposed response was: “No! No! Not a sixpence!”

When word of the French demands reached the United States, it caused an uproar and prompted calls for war. After some members of Congress asked to see the diplomats’ reports regarding what had transpired in France, Adams handed them over with the names of the French agents replaced with the letters X, Y and Z; thus the name XYZ Affair.

Congress subsequently authorized various defense measures, including the creation of the Department of the Navy and the construction of warships. Then, in July 1798, it authorized American ships to attack French vessels, launching an undeclared naval war that came to be referred to as the Quasi-War. The hostilities were settled with the Convention of 1800, also known as the Treaty of Mortefontaine, which was ratified in 1801.