The “hireling scribblers of the English press said little, and knew less,” wrote Thomas Jefferson to the Marquis de Lafayette on February 14, 1815. Long before President Donald Trump discovered fake news, Jefferson was already alluding to it. (Background: Impose Tariff On Justin Bieber, Ersjdamoo’s Blog, July 7, 2018.)
Much of the dreaded conspiracy thinking is found in Jefferson’s letter to Lafayette. There had been a “Hartford Convention” in Connecticut from December 15, 1814 through January 5, 1815. There, New England Federalists considered secession from the Union and alliance with Britain. Establishment historians (a.k.a. Court historians) now doubt that this was so, yet there is much evidence that yes, there indeed was a conspiracy underway to secede.  
At this Hartford Convention, wrote Jefferson to Lafayette, the New England Federalists were “playing the same game for disorganization here which they played in your country [France]. The Marats, the Dantons and Robespierres of Massachusetts are in the same pay, under the same orders, and making the same efforts to anarchize us, as their prototypes in France were.” 
It had been a conspiracy with Britain and against the Union. Certain “Henry Spy papers” suggested treason by Federalists on the eve of the War of 1812. Revelation of the Henry papers created much excitement throughout the country. “Oh, tut tut,” now say the Court historians, dismissive of “conspiracy theories” in general.  Yet original source documents point against the Court historians. See, for example, the letter, marked “Secret and Confidential”, from Lt. General John C. Sherbrooke to the Earl of Bathurst, dated November 20, 1814. 
John Henry (not the “steel drivin’ man” but a different John Henry) had arrived in Montreal in 1807 and communicated with one Herman Witsius Ryland regarding an American war with Britain leading to a dissolution of the Union. In 1809, Henry was sent to the United States on an official undercover mission. Between February 14th and May 22nd, 1809, Henry wrote 14 letters to the Canadian Governor which were forwarded to the colonial secretary, Lord Castlereagh. Henry concluded that in the event of war, the Federalist “Junto of Boston” would seek an alliance with Britain before seceding. 
The anonymous “B” (ascertained to have been Samuel F.B. Morse) describes John Henry as having been sent by Canada to Boston for the purpose of fomenting disaffection, destroying the Union, and “forming the eastern part thereof into a political connection with Great Britain.” 
——- Sources ——-
 “Hartford Convention”, Wikipedia. Accessed July 8, 2018. https://en.wikipedia.org/wiki/Hartford_Convention#Secession
 Evidence that an underlying secession scheme was underway can be found in the book, The War Of 1812, edited by Donald R. Hickey. Library Of America, 2013.
 “Thomas Jefferson to Marquis de Lafayette.” From The War Of 1812, edited by Donald R. Hickey. Library Of America, 2013. Page 682.
 “John Henry (spy)”, Wikipedia. Accessed July 8, 2018. https://en.wikipedia.org/wiki/John_Henry_(spy)
 Sherbrooke’s letter to Lord Bathurst, from The War Of 1812, edited by Donald R. Hickey. Library Of America, 2013. Page 594.
 “Henry, John”. Dictionary of Canadian Biography. http://www.biographi.ca/en/bio/henry_john_8E.html
 “The Present Attempt To Dissolve the American Union, A British Aristocratic Plot.” Pamphlet published in 1862. https://archive.org/details/presentattemptto00lcmors