Answer: They arranged the purchase of the Louisiana territory.
Louisiana Purchase was a deal between the USA and France and it was signed by Robert Livingston, James Monroe, and François Barbé-Marbois in the year 1803 on April 30th. This was announced by Jefferson on July 4th. Through this treaty 828,000 square miles of land west of the Mississippi River for $15 million was purchased . Due to this treaty USA got control over Missippi and New Orleans port.