The Foundation for the religion behind Christian nationalism was developed one hundred years before Hitler in the South. Evangelicals and Baptists came from a deliberately constructed religious system made by rich white enslavers to counteract the religious message of freedom and god from traveling preachers coming down from the North and Great Lakes who were preaching to poor whites and slaves.
By the time Hitler came along, the South Baptist and Southern evangelical churches had grown their own theological traditions that became embedded in the daily and Sunday cultural practices to become subtly pro-white and pro-Christian white God and white Jesus. It’s a historic evolution people apparently aren’t aware of if you haven’t read the original text and histories from then.