[Pelham]

You’d think that a nation born in secession from the United Kingdom would have taken that right as a given. Lincoln, like George III, turned an army on those who decided to leave.

If you compare King George III’s Speech to Parliament October 26, 1775 to Lincoln’s April 15, 1861 Proclamation raising an army to use against the states the difference is mainly George’s archaic and flowery verbiage. The content is the same.

[BroJoeK]

Pelham: "If you compare King George III’s Speech to Parliament October 26, 1775 to Lincoln’s April 15, 1861 Proclamation raising an army to use against the states the difference is mainly George’s archaic and flowery verbiage.
The content is the same."

Not really.
In February 1775, even before any open warfare, Parliament had already declared Massachusetts in rebellion.

Then King George's "Proclamation of Rebellion", August 23, 1775, came in response to the recent Battles of Lexington, Concord & Bunker Hill.
Worth noting that this was still almost a year before the American Declaration of Independence and Articles of Confederation, and at the time there were still many Americans (including Benjamin Franklin) who looked for ways to make peace with the Brits.
Also noteworthy that these battles began with British troops assaulting American positions.

By contrast, Lincoln's April 15, 1861 Proclamation came after Deep South secession and Confederacy, in response to the Confederate assault on Fort Sumter and Lincoln' Proclamation declared neither "rebellion" nor "insurrection".
Instead, Lincoln called for troops to "suppress said combinations" (referring to the 1807 Insurrection Act) and enforce US laws.
The words "insurrection" and "rebellion" came into official use later.