What Was the Burr Conspiracy?

Engraved portrait of Aaron Burr, the third Vice President of the United States.
Engraved portrait of Aaron Burr, the third Vice President of the United States.

Smith Collection/Gado/Getty Images

The Burr Conspiracy was a plot allegedly conceived by Aaron Burr in about 1804, while he was still Vice President of the United States under President Thomas Jefferson.

Key Takeaways: The Burr Conspiracy

  • The Burr Conspiracy was a plot conceived in 1804 by then-Vice President Arron Burr to carve out and lead a new, independent country in the Southwestern United States.
  • A strained relationship between Burr and President Thomas Jefferson left Burr bitter and largely ineffectual as vice president.
  • While still vice president, Burr attempted to get Britain to assist him in carrying out his plot.
  • Burr was secretly assisted by General James Wilkinson then Senior Officer of the U.S. Army.
  • Burr was eventually accused of treason and captured by federal troops in Louisiana on February 13, 1807.
  • Bush stood trial in Richmond, Virginia, in a court presided over by Chief Justice of the United States, John Marshall.
  • On September 1, 1807, Burr was acquitted due to the Constitution’s narrow definition of the act of treason.

According to the accusations against him, Burr sought to form and lead a new, independent country in the Southwestern United States and parts of Mexico. While his true intentions remain unclear and widely disputed among historians, most believe Burr’s goal was to take over parts of Texas and the newly acquired Louisiana Purchase for himself. Others believe he also hoped to conquer all of Mexico. Estimates of the number of men believed to have been committed to backing him vary from fewer than 40 to as many as 7,000.


Arron Burr was elected vice president by the U.S. House of Representatives after he and Thomas Jefferson had won an equal number of Electoral College votes in the 1800 presidential election

As vice president, Burr was largely ineffective due to being ignored by President Jefferson, who suspected that he had made secret deals with some Congressmen in an attempt to secure the presidency for himself. This strained relationship along with other incidents left Burr deeply unpopular among Jefferson’s Democratic-Republican Party leaders.

The Burr conspiracy probably began in early 1804, just months before Burr had killed Alexander Hamilton in their famous duel on July 11, 1804. With Burr’s hopes of ever becoming president already fading, they would vanish completely after killing Hamilton. Hoping to revive his political fortunes, Burr looked to the Louisiana Territory. Still mostly unsettled, the territory’s borders were still disputed by Spain and many of its new American settlers were agitating for secession. Burr believed that with the support of a small but well-armed military force he could turn Louisiana into his own empire. From there, he might even be able to grow his army and conquer Mexico.

Vice President Aaron Burr killing former Secretary of the Treasury Alexander Hamilton in a duel on July 11, 1804.
Vice President Aaron Burr killing former Secretary of the Treasury Alexander Hamilton in a duel on July 11, 1804.

Kean Collection/ Getty Images

In the summer of 1804, while still vice president, Burr had sent a message to Britain's Minister to the United States, Anthony Merry, offering to help Britain take the Western territories from the United States. Merry immediately contacted Britain of Burr’s plan to “effect a separation of the western part of the United States” from the rest of the Union. In return, Burr wanted the British to supply money and ships to help him in his conquest. In April 1805, Burr again approached Merry, this time falsely claiming that Louisiana was planning to secede from the United States. However, Britain’s new Foreign Secretary, Charles Fox, a friend of America, found Burr’s request treasonous, and on June 1, 1806, recalled Merry to Britain.

To build his military force without the assistance of Britain, Burr turned to the man who would become his foremost co-conspirator, General James Wilkinson then Senior Officer of the U.S. Army. Known for his arrogance and propensity for hard liquor, Wilkinson had befriended Burr during the American Revolution. Throughout his life, Wilkinson had been suspected of being a spy for Spain. During the 1780s, he had become known for trying to separate Kentucky and Tennessee from the Union to deliver them to Spain. President Theodore Roosevelt would later write of Wilkinson: “In all our history, there has been no more despicable character.” In early 1805, however, Burr convinced President Jefferson to appoint Wilkinson as the first Territorial Governor of Louisiana. To Burr, of course, this was like getting the farmer to put the fox in the henhouse. 

Portrait of General James Wilkinson, Senior Officer of the U.S. Army, 1800-1812.
Portrait of General James Wilkinson, Senior Officer of the U.S. Army, 1800-1812.

Independence National Historical Park/Wikimedia Commons/Public Domain

Despite his shortcomings, Wilkinson had much to contribute to Burr’s plans. The Army was in charge of maintaining law and order and of protecting settlers in the territories at the time. As commander of the Army, Wilkinson could move about Louisiana and the rest of the West without suspicion while secretly working to cultivate even more powerful support for Burr.  

Burr Roams the West

Shortly after his term as vice president ended in April 1805, Burr traveled through the West in search of supporters for his plot. In each of the many towns he visited, Burr encountered men that he thought would support him in his enterprise. One of them, he recruited Harman Blennerhassett, a man who would prove to be a particularly loyal follower. Blennerhassett was a flamboyant Irish gentleman who had come to America with a considerable fortune. He had built a mansion on an island in the Ohio River near Marietta, where he and his family lived a life of luxury. However, thanks to his involvement in Burr’s scheme, Blennerhassett’s paradise would soon be ruined.

Map illustrates former US Vice President Aaron Burr's approximate route during his trip down the Mississippi River in what became known as the Burr conspiracy in 1806-1807
Map illustrates former US Vice President Aaron Burr's approximate route during his trip down the Mississippi River in what became known as the Burr conspiracy in 1806-1807.

Interim Archives/Getty Images

By the time he returned to Washington in November 1805, Burr had collected had several backers, including former U.S. Senator and Representative, Jonathan Dayton, who had signed the U.S. Constitution in 1787, and a group of well-off New Orleans businessmen who favored the further annexation of Mexican territory in the Western U.S. 

Despite Burr’s success at obtaining financial backing, problems remained. Military support from Britain and Spain had not and never would arrive. Worse yet, Eastern newspapers had started publishing rapidly spreading rumors of his plot. Yet Burr pressed on.

Meanwhile, during 1805 and 1806, the long-simmering dispute with Spain over the exact borders of the Louisiana Territory began to heat up. When diplomatic negotiations broke down, Burr figured Jefferson would order Wilkinson to take federal troops to Louisiana. This would enable Wilkinson and Burr to attack Texas or even Mexico under the guise of enforcing U.S. sovereignty. Burr could then declare himself to be the ruler of the conquered lands.

Now feeling confident to move forward, Burr sent a coded letter to Wilkinson outlining his plans. Now infamously known as the Cipher Letter, the document would later play a significant role in Burr’s treason trial. In August 1806, Burr ordered Harman Blennerhassett to convert his private Ohio River Island and mansion into a military encampment to house his troops. 

Unrest and Arrest 

Burr’s plot, like his life, began to unravel quickly in March of 1806. As the trickle of rumors about his plans became a torrent, Joseph H. Daveiss, a Kentucky Federalist, wrote Jefferson several letters warning him of possible conspiratorial activities by Burr. Daveiss’s July 14, 1806 letter to Jefferson stated flatly that Burr planned to provoke a rebellion in Spanish-held parts of the West and Southwest to form an independent nation under his rule. Jefferson, however, dismissed Daveiss’ accusations against Burr, a fellow Republican, as being politically motivated.

In September 1806, a variety of sources in Pennsylvania and New York, including Generals William Eaton and James Wilkinson, sent Jefferson further information confirming that Burr was organizing a military expedition against Spanish possessions for the purpose of separating western territories from the United States. While Wilkinson provided information about the conspiracy after having been implicated in it himself, he did not specifically name Burr.

In November 1806, Jefferson responded by issuing a proclamation declaring that “sundry persons, citizens of the U.S. or resident within the same, are conspiring and confederating ... against the dominions of Spain” and requiring that all military and civil officials of all states and territories of the United States prevent “the carrying on such expedition or enterprise by all lawful means within their power.” While Jefferson never specifically named Burr, he didn’t need to. By this time, the newspapers were full of treason talk, with Burr’s name prominently featured. 

Acting on Jefferson’s proclamation, the U.S. District Court in Frankfort, Kentucky, called Burr to stand before the court three times to answer charges of treason. Each time he was acquitted.

The first blow against Burr came on December 9, 1806, when Ohio militiamen captured most of his boats, arms, and supplies at a Marietta boatyard. On December 11, the militia raided Blennerhassett’s Ohio River Island. While most of Burr’s men—who totaled no more than 100—had already fled downriver, Blennerhassett’s mansion was ransacked and set ablaze. 

At Bayou Pierre, 30 miles north of New Orleans, Burr was shown a New Orleans newspaper article announcing a reward for his capture along with a full translation of the coded letter he had sent to Wilkinson. 

After surrendering to authorities at Bayou Pierre, Burr was arraigned before a grand jury. When he testified that he had no intention of attacking U.S. territory, the jury failed to return an indictment. However, one of the judges ordered Burr returned to the courtroom. Convinced he would ultimately be indicted, Burr fled into the wilderness.

Place where Aaron Burr was captured, near Wakefield, Alabama.
Place where Aaron Burr was captured, near Wakefield, Alabama.

Wikimedia Commons/Public Domain

On February 13, 1807, a soaking wet and disheveled Burr was captured by U.S. soldiers from Ft. Stoddert, Louisiana Territory as he walked along a muddy road near the village of Wakefield, Alabama. Now disgraced, the former Vice President of the United States would be carried back to the federal court at Richmond, Virginia, to stand trial for treason.

The Treason Trial

On March 26, 1807, Burr arrived in Richmond, where he was held under guard in room in the Eagle Hotel. Four days later he was brought to another room in the hotel for an examination before the judge who would conduct his trial—none other than the Chief Justice of the United States, John Marshall.

Shortly after noon on May 22, 1807, the treason trial of Aaron Burr began. In what was truly the trial of the century, Aaron Burr battled for his life. Both the prosecution and the defense, led by Edmund Randolph and Luther Martin, both delegates to the Constitutional Convention—depended heavily on passages from the Cipher Letter Burr had sent to Wilkinson. However, the Cipher Letter was trumped by an even more definitive document: the U.S. Constitution, in which Article III, Section III defines treason as consisting only of “levying War” against the United States. On August 20, Burr’s defense asked the court to dismiss further prosecution testimony on the ground that the evidence had “utterly failed to prove any overt act of war had been committed.”

Supreme Court Justice John Marshall insisted on absolute adherence to the Constitution’s strict definition of the act of treason, which Burr's actions had not met. Marshall concluded that the prosecution failed to produce sufficient evidence of treason. Marshall’s decision ended the prosecution's case and the case was sent to the jury. In his final instructions to the jury, Marshal stated that for Burr to be found guilty, the prosecution had to have proven that there had been an "actual use of force" and that Burr was “connected to that use of force.” In effect, Marshall demanded that the government prove what it could not prove.

On September 1, 1807, the verdict was read: “We of the jury say that Aaron Burr is not proved to be guilty under this indictment by any evidence submitted to us. We therefore find him not guilty.” While they had little choice, the members of the jury hinted that they might have decided the case differently had it not been for the Marshall’s instructions.

Despite his acquittal, Burr was disgraced. He was burned in effigy across America and several states filed additional charges against him. Living in fear for his life, Burr fled to Europe, where he reportedly tried without success to convince Britain and France to support other North American invasion plots.

When Burr returned to America in mid-1812, the country was on the brink of war with Britain, and the Burr Conspiracy had been all but forgotten. The death of his beloved daughter Theodosia, lost at sea while sailing to meet her father in New York upon his return, seemed to extinguish whatever spark for grandeur remained within Burr. Never again to be a significant player in American public life, Burr settled in New York, where he established himself as an attorney. After reading news of U.S. support of the Texas Revolution against Mexico in 1835, Burr exclaimed to a friend with satisfaction, “There! You see? I was right! I was only thirty years too soon. What was treason in me thirty years ago, is patriotism now.”

A lasting legacy of Burr’s role in the election of 1800—the Twelfth Amendment to the Constitution—changed how vice presidents were to be chosen. As shown in the 1800 election, how the president and vice president were chosen at the time, the situation where the vice president, as the defeated presidential candidate, might not work well with the president could easily arise. The Twelfth Amendment required that electoral votes be cast separately for president and vice president.

Arron Burr died of a stroke on September 14, 1836, on Staten Island in the village of Port Richmond, while living in a boardinghouse that later became the St. James Hotel. He was buried near his father in Princeton, New Jersey. 


  • Lewis, James E. Jr. “The Burr Conspiracy: Uncovering the Story of an Early American Crisis.” Princeton University Press, Oct 24, 2017, ISBN: 9780691177168.
  • Brammer, Robert. “General James Wilkinson, the Spanish Spy Who was a Senior Officer in the U.S. Army During Four Presidential Administrations.” Library of Congress, April 21, 2020, https://blogs.loc.gov/law/2020/04/general-james-wilkinson-the-spanish-spy-who-commanded-the-u-s-army-during-four-presidential-administrations/. 
  • Linder, Douglas O. “Ciphered Letter of Aaron Burr to General James Wilkinson.” Famous Trials, https://www.famous-trials.com/burr/162-letter.
  • Wilson, Samuel M. “The Court Proceedings of 1806, In Kentucky Against Aaron Burr and John Adair.” The Filson Club History Quarterly, 1936, https://filsonhistorical.org/wp-content/uploads/publicationpdfs/10-1-5_The-Court-Proceedings-of-1806-in-Kentucky-Against-Aaron-Burr-and-John-Adair_Wilson-Samuel-M..pdf.
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Longley, Robert. "What Was the Burr Conspiracy?" ThoughtCo, Mar. 30, 2022, thoughtco.com/burr-conspiracy-5220736. Longley, Robert. (2022, March 30). What Was the Burr Conspiracy? Retrieved from https://www.thoughtco.com/burr-conspiracy-5220736 Longley, Robert. "What Was the Burr Conspiracy?" ThoughtCo. https://www.thoughtco.com/burr-conspiracy-5220736 (accessed June 4, 2023).