U.S.A. vs United States

U.S.A.

name
  • Dated spelling of USA. 

United States

name
  • The collection of individual states of the United States of America. 

  • Federal nation consisting of several states, actual, historical or hypothetical. 

  • Includes the land area, internal waters, territorial sea, and airspace of the United States. 

How often have the words U.S.A. and United States occurred in a corpus of books? (source: Google Ngram Viewer )