The United States declared war on the first Barbary War.

180 1 On the eve of Jefferson's inauguration, Congress passed a new naval legislation: six additional frigates were provided to the President, who could directly command them and order them to carry out manned instructions. Under the tension that the United States and the Barbary powers are about to declare war, these ships were sent to the Libyan coast to protect American commerce, fulfill their maritime obligations, and were ordered to destroy enemy ships under any circumstances. 180 1 year, Jefferson officially became president, and Pasha (or governor) of Tripoli demanded $225,000 from the new government (1800, the total federal income was slightly higher than 100000). But Jefferson insisted on his consistent belief and refused this request. Soon, Yusuf Karamanle declared war on the United States. Yusuf Karamanle didn't announce the start of the battle through official paper documents, but cut down the flagpole in front of the American consulate in the traditional way of Babari. Neighbouring Algeria and Tunisia did not follow Tripoli's example.

In response, Jefferson sent a small army to Tripoli to protect American ships and citizens, but Congress insisted that he crossed the line without the approval of the Constitution and Congress. Jefferson told Congress: I have provided you with all the information about this war. When you exercise your important functions, you should make use of your knowledge, see the situation clearly and weigh it carefully. Although Congress did not vote for a formal declaration of war, they authorized the President to instruct commanders to arm ships and seize all ships and goods in Tripoli Pasha.

180 1 year 1 month, after fierce fighting, sailing enterprises defeated the Tripoli pirate ship with 14 shelling. 1802, in response to Jefferson's power demand in dealing with piracy, Congress passed a new decree: allowing the president to use armed vessels to defend the safety of American sailors and enterprises in the Atlantic Ocean, the Mediterranean Sea and nearby waters. This law authorizes American ships to detain ships belonging to Tripoli Bay and distribute the seized property to those who bring the ships into the port.

Despite this, the US Navy's questioning of the sea surface remains unresolved. Jefferson pressed Congress on this issue in 1803, and gained more troops in Tripoli, deploying many of the best warships in China, such as argus, Schabik, Constellation, Constitution, Enterprise, Intrepid, Philadelphia and Witch. During the whole period of 1803, Preble established and maintained the blockade of ports in North Africa, and carried out a series of raids and attacks on cities.