Confederate States of America vs Southern United States

Confederate States of America

name
  • An unrecognized nation existing from 1861–1865, consisting of the eleven Southern states who sought independence from the United States of America over the issue of slavery. 

Southern United States

name
  • An expansive region encompassing the southeastern and south-central part of the United States, typically defined as including the states of Texas, Oklahoma, Louisiana, Arkansas, Alabama, Mississippi, Tennessee, Kentucky, Florida, Georgia, North Carolina, South Carolina, West Virginia, and Virginia, sometimes also Maryland, Delaware, Washington, D.C., and Missouri. 

How often have the words Confederate States of America and Southern United States occurred in a corpus of books? (source: Google Ngram Viewer )