Southern United States vs the South

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. 

the South

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