The July 29, 1806 letter was the thing that undid the Burr Conspiracy.
Harman Blennerhassett had been a moderately well off Anglo-Irish aristocrat prior to his becoming involved with Irish revolutionaries in the last decade of the 18th century. Fearing that British authorities might arrest him, he sold his property in Ireland and bounded for the United States with his wife Margaret.
In 1799 Blennerhassett bought half the island that now bears his name, an island on the Ohio River below the mouth of the Little Kanawha River, located near Parkersburg, WV. Blennerhassett and his wife proceeded to build a mansion on the island, where they entertained neighbors and any notables that came by.
In May 1805 Aaron Burr, former Vice President of the United States, and victor in the duel in which he killed Alexander Hamilton, visited the Blennerhassett home.
After the visit Blennerhassett wrote to Burr:
“I should be honored in being associated with you, in any contemplated enterprise you would permit me to participate in….Viewing the probability of a rupture with Spain,…I am disposed, in the confidential spirit of this letter, to offer you and my friends’ and my own services in any contemplated measures in which you may embark.”
Using the 300 acre island as a staging ground, Burr aimed to form a new country fashioned from the Louisiana Purchase territories. He also proposed to conquer Texas and the rest of Mexico to add to this western nation. Apparently Burr found a friend in Blennerhassett—during one conversation the Irishman told Burr he would be King Aaron I of Mexico and his daughter Theodosia would be a princess.
By the end of August 1806, Burr returned to Blennerhasset’s Island, making final preparations for his expedition. Burr brought with him to the island a force of less than fifty men, which he planned to be the nucleus of a conquering army. He contracted to purchase fifteen boats capable of carrying 500 men, and a large keel boat for transporting provisions. He made orders for huge quantities of pork, corn meal, flour, and whiskey. Burr and his men planned to head down the Mississippi to confer with James Wilkinson, the U.S. Army’s ranking general and one of Burr’s oldest friends, then in New Orleans.
In early October, a ciphered letter sent by Burr reached Wilkinson in New Orleans.
I have obtained funds, and have actually commenced the enterprise. Detachments from different points under different pretenses will rendezvous on the Ohio, 1st November– everything internal and external favors views–protection of England is secured.
T[ruxton] is gone to Jamaica to arrange with the admiral on that station, and will meet at the Mississippi– England—Navy of the United States are ready to join, and final orders are given to my friends and followers–it will be a host of choice spirits. Wilkinson shall be second to Burr only–Wilkinson shall dictate the rank and promotion of his officers.
Burr will proceed westward 1st August, never to return: with him go his daughter–the husband will follow in October with a corps of worthies. Send forthwith an intelligent and confidential friend with whom Burr may confer. He shall return immediately with further interesting details–this is essential to concert and harmony of the movement….
[T]he project is brought to the point so long desired: Burr guarantees the result with his life and honor–the lives, the honor and fortunes of hundreds, the best blood of our country. Burr’s plan of operations is to move rapidly from the falls on the 15th of November, with the first five hundred or one thousand men, in light boats now constructing for that purpose–to be at Natchez between the 5th and 15th of December–then to meet Wilkinson–then to determine whether it will be expedient in the first instance to seize on or pass by Baton Rouge.
On receipt of this send Burr an answer–draw on Burr for all expenses, &c. The people of the country to which we are going are prepared to receive us–their agents now with Burr say that if we will protect their religion, and will not subject them to a foreign power, that in three weeks all will be settled.
The gods invite to glory and fortune–it remains to be seen whether we deserve the boon…. –29th July.
But Wilkinson saw the new army’s dark future. British Prime Minister William Pitt had recently died and Wilkinson learned of Charles Fox taking over the government. This would end British support for the expedition and ultimately drive it to the ground. He panicked, and dropped out of Burr’s conspiracy.
Wilkinson instead rushed troops to the Mississippi Valley and ordered troops in New Orleans to be on alert for an attack. He sent Burr’s ciphered letter (in decoded form), together with one from another co-conspirator, to President Thomas Jefferson.
A militia detachment of thirty men caught up with Burr when he and his expedition of between sixty and hundred men were camped across from Natchez, on the west bank of the Mississippi. Burr was handed a letter from the Governor of Mississippi demanding his surrender. Burr responded to the letter by denouncing Wilkinson, whose “perfidious conduct” had “completely frustrated” his “projects.”
Meanwhile Ohio and Virginia militias were sent to stop boat traffic on the Ohio and Muskingum Rivers and seize the Blennerhassett home. Blennerhassett escaped down the river, and his wife, after much difficulty with the invaders, followed him with their three children. The mansion was heavily damaged by the militiamen, who were no doubt frustrated by the elusive Blennerhassett. But when Blennerhassett tried to return to recover some of the furnishings he too was arrested.
The government had no problem proving that Burr raised money and men on Blennerhasset Island. The only problem was that they could not work the evidence into anything higher than a misdemeanor charge. As a result the trial, conducted by Chief Justice John Marshall, resulted in acquittal of both men on the grounds that Burr had never committed an overt act, as required by the constitutional definition of the offense.
The Blennerhassett mansion burned in 1809.
During the 1980s, the mansion was reconstructed on its original foundations. Today the island is the site of Blennerhassett Island Historical State Park.