俺也是偶然跟娃聊历史课时才主意到这个现象的。刚刚查了一下Wikipedia...

By 1876, "Redeemer" Democrats had taken control of all state governments in the South. From then until the 1960s, state and local government in the South was almost entirely monopolized by Democrats. 

https://en.m.wikipedia.org/wiki/Solid_South