The tribes sided with the Confederates because they were upset that the US Government removed them from their land the US military abandoned the post in Indian Territory at the start of the Civil War, leaving the tribes unprotected the tribes more aligned to the agriculture economy of the South all of the above

The tribes sided with the Confederates because they were upset that the US Government removed them from their land the US military abandoned the post in Indian Territory at the start of the Civil War, leaving the tribes unprotected the tribes more aligned to the agriculture economy of the South all of the above