My point was that I’m unsure on the practical difference at the time. Were these part-time soldiers on a weekend raid, like we usually think of the milita, a Home Guard, if you will, or were they full-time soldiers just like those fighting back east, only Volunteers instead of Regulars?
If the first, then the distinction between Regulars and militia is significant. If the second, then IMO it is not and the US Army is fully responsible.
At the time, something over 95% of Union army were Volunteers.
Every time I have ever looked into Sand Creek, it always looked like Chivington and his drunken Colorado guys were on their own crazy massacre in the Colorado territory,
Chivington was forced to resign from the militia, and was banned from Colorado politics, politics which had always been his purpose.