Gaining Louisiana terrified many Federalists, who feared that the creation of new western states would further weaken their political power. In the winter of 1803-1804, a group of Federalist congressmen plotted to establish a "Northern Confederacy" consisting of New Jersey, New York, New England, and Canada, to be established with the support of Britain.
Alexander Hamilton disapproved of this scheme, and the plotters turned to Vice President Aaron Burr. In return for Federalist support in his campaign for the governorship of New York, Burr was to swing New York into the Northern Confederacy. Burr was badly beaten, in part because of Hamilton's opposition. Extremely angry, Burr challenged Hamilton to the duel in which the former Treasury Secretary was fatally wounded.
Burr was now a ruined politician and a fugitive from the law. In debt, on the edge of bankruptcy, his fortunes at their lowest point, the desperate Burr became involved in a conspiracy (plot) for which he would be put on trial for treason.
In the spring of 1805, Burr traveled to the West, where he and an old friend, James Wilkinson, commander of United States forces in the Southwest and military governor of Louisiana, planned a mysterious scheme. It is still uncertain what the plotters goal was, since Burr told different stories to different people. Spain's minister believed that Burr planned to set up an independent nation in the Mississippi Valley. Others reported that he planned to take Spanish territory in what is now Texas, California, and New Mexico. The British minister was told that for $500,000 and British naval support, Burr would separate the states and territories west of the Appalachians from the rest of the Union and create an empire with himself as its head.
In the fall of 1806, Burr and some 60 schemers traveled down the Ohio River toward New Orleans, perhaps to get the unhappy French settlers to revolt. Wilkinson, recognizing that the scheme was doomed to failure, sent a letter to President Jefferson betraying Burr.
Burr fled, but was captured in Mississippi Territory. He was then taken to the Richmond, Virginia, circuit court, where, in 1807, he was tried for treason. Jefferson, convinced that Burr was a dangerous man, wanted a conviction regardless of the evidence. Chief Justice John Marshall, the chief justice, was equally eager to ruin Jefferson.
Burr was acquitted (not found guilty). The reason for the acquittal was the Constitution's strict definition of treason as "levying war against the United States" or "giving ... aid and comfort" to the nation's enemies. In addition, each obvious act of treason had to be declared to by two witnesses. The prosecution was unable to meet this strict standard, and as a result of Burr's acquittal, few future cases of treason have ever been tried in the United States.
Was Burr guilty of conspiring to separate the West by force? Probably not. The prosecution's case was extremely weak. It rested largely on the unreliable testimony of co-plotter James Wilkinson, who was a spy in the way of Spain while serving as a U.S. army commander and governor of Louisiana.
What, then, was the purpose of Burr's scheming? It appears likely that the former vice president was planning a an unauthorized military attack on Mexico, which was then controlled by Spain. To the end of his life, Burr denied that he had plotted treason against the United States. Asked by one of his closest friends whether he had sought to separate the West from the rest of the nation, Burr responded with an forceful "No! I would as soon have thought of taking possession of the moon and informing my friends that I intended to divide it among them."