Burr’s Conspiracy Summary

  • Last updated on November 10, 2022

In one of the least understood events in early American national history, Aaron Burr plotted to invade Mexico and detach the Mississippi Valley from the United States. His challenge to the territorial integrity of the new Union failed, but from it emerged a Supreme Court decision that mere intent cannot in itself be considered treasonous.

Summary of Event

From 1804 through 1806, Aaron Burr promoted, organized, and led an expedition into the Mississippi Valley. Although his purpose remains unclear, he may have intended to invade Spanish Mexico, detach several western states from the union, colonize in what is now northwestern Louisiana, or some combination of these goals. In addition, he was accused of plotting to overthrow the U.S. government and seize Washington, D.C. Burr, Aaron [p]Burr, Aaron;conspiracy Mexico;and Aaron Burr[Burr] Treason;Aaron Burr[Burr] Wilkinson, James [kw]Burr’s Conspiracy (Mar., 1805-Sept. 1, 1807) [kw]Conspiracy, Burr’s (Mar., 1805-Sept. 1, 1807) Burr, Aaron [p]Burr, Aaron;conspiracy Mexico;and Aaron Burr[Burr] Treason;Aaron Burr[Burr] Wilkinson, James [g]United States;Mar., 1805-Sept. 1, 1807: Burr’s Conspiracy[0270] [c]Government and politics;Mar., 1805-Sept. 1, 1807: Burr’s Conspiracy[0270] [c]Wars, uprisings, and civil unrest;Mar., 1805-Sept. 1, 1807: Burr’s Conspiracy[0270] [c]Crime and scandals;Mar., 1805-Sept. 1, 1807: Burr’s Conspiracy[0270] Alston, Theodosia Burr Blennerhassett, Harman Jackson, Andrew [p]Jackson, Andrew;and Aaron Burr[Burr] Jefferson, Thomas [p]Jefferson, Thomas;and Aaron Burr[Burr] Marshall, John [p]Marshall, John;and Aaron Burr[Burr] Yrujo, Marqués de Casa Merry, Anthony

Burr had been prominent in the American Revolution (1775-1783) and was a generally successful politician noted for ambition, elegance, womanizing, and opportunism. After he was rejected for a second term as vice president by Thomas Jefferson Jefferson, Thomas [p]Jefferson, Thomas;and Aaron Burr[Burr] Burr, Aaron [p]Burr, Aaron;and Thomas Jefferson[Jefferson] and the Republicans, he was defeated in a bid for governor of New York in 1804. Shortly thereafter, James Wilkinson, commanding general of the Army, requested a visit and surreptitiously spent the night at Burr’s residence. What transpired is unclear, but it is thought they laid plans to conquer Texas Texas;and Aaron Burr[Burr] and northern Mexico, and may have discussed separating the western lands from the United States.

Angered by Alexander Hamilton’s Hamilton, Alexander [p]Hamilton, Alexander;and Aaron Burr[Burr] derogatory personal remarks during the gubernatorial campaign, Burr challenged Hamilton to a duel and killed him on July 11, 1804. The election and duel effectively terminated Burr’s political career. To escape arrest, Burr fled to Philadelphia, where he met Charles Williamson Williamson, Charles , an old friend and a British agent. He discussed his western plans with Williamson, who presented them to Anthony Merry Merry, Anthony , the British minister to the United States. Merry forwarded Burr’s plan to detach the western states and invade Mexico to his superiors in London, who were uninterested. Many historians believe Burr also met Wilkinson in Philadelphia and, at that time, concocted his conspiracy. Wilkinson’s presence in Philadelphia, however, is unverified in public accounts. Burr resumed his vice presidential duties on November 4, 1804, in spite of outstanding indictments for murder in New York and New Jersey. Apparently furthering his plans, Burr influenced Jefferson Jefferson, Thomas [p]Jefferson, Thomas;and Aaron Burr[Burr] Burr, Aaron [p]Burr, Aaron;and Thomas Jefferson[Jefferson] to appoint Wilkinson governor of the northern part of the District of Louisiana at St. Louis.

On March 2, 1805, Burr withdrew from the Senate. He then met with Merry and offered to detach Louisiana (at that time, the huge region extending from the Great Lakes to the Gulf of Mexico, bordered on the east by the Mississippi River and on the west by the Great Plains) from the United States. His price for doing so would be one-half million dollars and British naval support in the Gulf of Mexico. Merry Merry, Anthony again wrote to his superiors on March 29, but received no response.

On April 23, Burr set out for Pittsburgh and the Ohio and Mississippi Valleys, seeking support and widely discussing his various plans. On his way down the Ohio River Ohio River , he visited the estate of Harman Blennerhassett, Blennerhassett, Harman a wealthy and idealistic Irish expatriate, who subsequently became one of Burr’s principal supporters. He also met twice with Andrew Jackson Jackson, Andrew [p]Jackson, Andrew;and Aaron Burr[Burr] , who commanded the Tennessee militia at Nashville, enlisting his support for a campaign against the Spanish lands. He conferred with Wilkinson at Fort Massac, just below the junction of the Cumberland and Ohio Rivers, on June 6 and probably refined the plan to invade Mexico. In New Orleans, he contacted the Mexican Associates, Mexican Associates a group of Creoles and the bishop of New Orleans, securing encouragement for an expedition against Mexico. On his return trip, Burr spent several days with Wilkinson in St. Louis in September, 1805, and apparently made more detailed plans for invading Mexico.

After returning to Washington in November, 1805, Burr and his associates unsuccessfully sought aid from the Marqués de Casa Yrujo, Marqués de Casa Yrujo, the Spanish minister to the United States, to dismember the union and establish an independent western confederacy. In July, 1806, Burr purchased the Bastrop lands, about four hundred thousand acres on the Washita River Washita River in northwestern Louisiana. He then went west again to recruit volunteers and support for a military expedition down the Mississippi River, which he planned for late fall.

Dispersal of Burr’s expedition.

(C. A. Nichols & Company)

As Burr was developing his plans, President Jefferson Jefferson, Thomas [p]Jefferson, Thomas;and Aaron Burr[Burr] Burr, Aaron [p]Burr, Aaron;and Thomas Jefferson[Jefferson] ignored the detailed reports he was receiving of Burr’s activities. Nevertheless, on November 4, Burr was brought before a grand jury in Frankfort, Kentucky, charged with preparing a military expedition against Mexico but was declared innocent the next day. In the meantime, Harman Blennerhassett Blennerhassett, Harman converted his island estate on the Ohio River opposite what is now Parkersburg, West Virginia, into a supply depot and rendezvous site for Burr’s recruits. This activity attracted the attention of the governor of Ohio, who sent the state militia to seize the island and most of Blennerhassett’s supplies on December 5. Meanwhile, Burr went to Nashville, reassured Andrew Jackson, Jackson, Andrew [p]Jackson, Andrew;and Aaron Burr[Burr] obtained boats from Jackson, and rejoined his group at the mouth of the Cumberland River on December 27. Accompanied by about sixty men on December 29, he appeared below Fort Massac, explaining that his purpose was to colonize the Bastrop lands that he had legally purchased.

Meanwhile, Wilkinson apparently lost confidence in Burr’s plan and informed Jefferson of the scheme to dismember the United States. Wilkinson also sent Jefferson Jefferson, Thomas [p]Jefferson, Thomas;and Aaron Burr[Burr] Burr, Aaron [p]Burr, Aaron;and Thomas Jefferson[Jefferson] a “cipher letter,” purportedly from Burr, detailing Burr’s plans. He also declared martial law in Louisiana and arrested some of Burr’s associates. Jefferson then ordered the arrest of anyone conspiring to attack Spanish territory. Learning of the president’s order at Natchez, Burr attempted to flee to Spanish Florida. He was arrested near Mobile, brought to Richmond, Virginia, and arraigned on charges of treason for attempting to dismember the union and of the misdemeanor of organizing an expedition against Spanish territory.

Chief Justice John Marshall Marshall, John [p]Marshall, John;and Aaron Burr[Burr] , who presided over Burr’s Burr, Aaron [p]Burr, Aaron;trial of subsequent trial, interpreted the U.S. Constitution narrowly, ruling that the mere expression of intent to divide the union did not constitute an overt act of treason. Government witnesses, some of whom were successfully contradicted, and the “cipher letter” failed to demonstrate overt acts of treason by Burr, so Marshall dismissed the treason charge against Burr. The government was unable to prove that Burr’s expedition had been military or had been directed against Spanish territory, so the misdemeanor charge was dropped as well.

After his release, Burr spent four years in Europe lobbying the British and French governments to support his Mexican plans. After returning to the United States, he practiced law in New York. Wilkinson was investigated by Congress and court-martialed by the army but was cleared and retained his command.


Although Burr discussed his plans with hundreds of people, the true story of his conspiracy remains controversial. Until his death, he continued to promote diverse settlement schemes and expeditions into Spanish and Mexican territory. Documents relating to his plans that have survived are wildly contradictory, unreliable, and incomplete. His daughter, Theodosia Burr Alston Alston, Theodosia Burr , the only person whom he fully trusted, was lost at sea with a large collection of his papers in 1813. Burr willed his other personal papers to Matthew L. Davis, a politician, journalist, and friend, but they were partly destroyed and lost.

Burr’s alleged goals were by no means unique. Secession was repeatedly proposed to advance regional interests until the Civil War (1861-1865). Private American filibustering excursions into Spanish and Mexican territory persisted until after the Spanish American War (1898). A mature sense of national identity did not come to the United States until the late nineteenth and early twentieth centuries.

Burr’s case also had important constitutional ramifications. Chief Justice Marshall’s Marshall, John [p]Marshall, John;and Aaron Burr[Burr] Burr, Aaron [p]Burr, Aaron;trial of ruling in Burr’s favor preserved the right of Americans to voice opposition to the government without fear of being charged with treason and further defined the independent scope of the judicial and executive branches of government.

Further Reading
  • citation-type="booksimple"

    xlink:type="simple">Adams, Henry. History of the United States of America During the Administrations of Jefferson and Madison. 9 vols. New York: Charles Scribner’s Sons, 1889-1891. After examining English and Spanish archives, Adams concluded that Burr conspired to dismember the union; his conclusion gained wide acceptance.
  • citation-type="booksimple"

    xlink:type="simple">Brodie, Fawn M. Thomas Jefferson: An Intimate History. New York: Bantam, 1974. This distinguished biography of Jefferson suggests that Burr’s many conflicting purported plots and unfounded claims resulted from mental imbalance on his part.
  • citation-type="booksimple"

    xlink:type="simple">Fleming, Thomas J. Duel: Alexander Hamilton, Aaron Burr, and the Future of America. New York: Basic Books, 1999. Lively study of the political rivalry between Burr and Hamilton that is placed firmly within the chaotic political environment of the time.
  • citation-type="booksimple"

    xlink:type="simple">Lomask, Milton. Aaron Burr: The Conspiracy and Years of Exile, 1805-1806. New York: Farrar, Straus and Giroux, 1982. Based on primary documents and scholarly analyses of older records, including a discrediting of Burr’s purported “cipher letter” to Wilkinson.
  • citation-type="booksimple"

    xlink:type="simple">Melton, Buckner F., Jr. Aaron Burr: Conspiracy to Treason. New York: John Wiley & Sons, 2002. Study of Burr’s plot to set up an independent republic in the western United States or Mexico. A constitutional law expert, Melton provides a detailed account of Burr’s treason trial.
  • citation-type="booksimple"

    xlink:type="simple">Montgomery, M. R. Jefferson and the Gun-men: How the West Was Almost Lost. New York: Crown, 2000. Popular account of Burr’s conspiracy.
  • citation-type="booksimple"

    xlink:type="simple">Parmet, Herbert S., and Marie B. Hecht. Aaron Burr: Portrait of an Ambitious Man. New York: Macmillan, 1967. A well-documented biography of one of the most enigmatic figures in American history.
  • citation-type="booksimple"

    xlink:type="simple">Vidal, Gore. Burr. New York: Random House, 1973. Well-documented historical novel, in which fact and fiction are clearly separated. Re-creates the contemporary social and political environment during Burr’s lifetime. Vidal is remotely related to Burr.

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Categories: History