Quite true. It WAS an attempt to put down a rebellion.
It’s just that the attempt failed, so none dare call it rebellion.
No doubt the American Revolution was a rebellion. The reasons were laid out in the Declaration of Independence.
In imitation of that, the so called confederates wrote their resolutions of secession and various other documents.
The difference: The confederate cause was less convincing, and so they had more trouble convincing people to help them.
And the Continentals won, while the confederates lost.