My question is prompted by current events, but I would like to know, historically, where has the dividing line been?
For reference, Article III, Section 3 states: "Treason against the United States, shall consist only in levying war against them, or in adhering to their enemies, giving them aid and comfort. No person shall be convicted of treason unless on the testimony of two witnesses to the same overt act, or on confession in open court."
The constitution also contemplates rebellion and insurrection, and gives the president and congress certain powers which are distinct from the powers related to warfare.
So, my question is: where has the line been drawn between rebellion and treason? At what point, if ever, has the government held that citizens have gone beyond insurrection and have committed an "overt act" of "levying war" against the states? Did the Whiskey Rebellion give rise to formal charges of Treason? Did the Civil War? Are there other precedents that would be informative?
At risk of stating the obvious, all three terms are bandied about in politically charged situations by politicians with an agenda.
That being said, treason is a specifically defined crime of which a person can be convicted in a court of law (think Benedict Arnold). As the Constitution you cited says, conviction for treason requires the testimony of at least two witnesses. That is one main difference when it comes to sedition, an offense created by later acts like the Alien and Sedition Acts of 1798 or the Espionage Act of 1917. Sedition as an offense is more broadly defined and lowers the burden of proof, thus making it easier for the government to 'prove' sedition on the part of the accused.
As for rebellion and insurrection, which are not as clearly defined in a legal sense, the words contemplate the taking up of arms and an open animosity toward the existing government. They aren't criminal offenses in the pure sense, but are used to indicate a state of organized resistance to the government, mainly as a way to indicate the necessity of the government's armed response to quell the rebellion.
Black's Law Dictionary is instructive in defining these terms as well.
As for examples, the Whiskey Rebellion resulted in several charges of Treason and a few resulting convictions, but Washington later pardoned those men. [source]
The Burr Conspiracy and trial is another example of a trial for treason, but because the prosecution lacked two testifying witnesses, Burr was acquitted.
The Civil War is an altogether different animal. There were certainly prosecutions for treason. One well known case was Ex parte Merryman, involving John Merryman who'd burned railroad bridges in Baltimore before the outbreak of the war and who was then imprisoned. Anyway, the trial centered on habeus corpus, the issue for which it is remembered, but Merryman was later charged with treason. The charges were dropped in 1867 and no trial was ever held. [source]
There were also the Indianapolis Treason Trials, summarized in this article by William Rehnquist. The bottom line it seems with the Civil War is that many treason trials were initiated during the war, but by the time it was over public sentiment had shifted away from harsh punishments and toward a more lenient approach. The treason trials followed that sentiment for the most part and many actors that could have been convicted of treason were simply not prosecuted after the war.
I can't answer well enough for this sub, but please throw "sedition" in there, too, since it may be relevant, both to current events and the legal history of criminal anti-government activity.