He accumulated wealth in lumber and coal mine interests in Bolling, Alabama.
As a railroad engineer, he was the principal player in choosing site of the City of Birmingham, based on his assessment of the strategic resources and transportation advantages of Jones Valley in Alabama.
Milner's vision triggered decades of rapid industrial growth.
After emancipation, Milner was instrumental in the movement of industrialists to replace slavery with "convict" Black laborers.
He found that it was impossible to drive "free" labor the same way that they could force prisoners to mine and build railroad infrastructure.