All's fair in love and war

Does anyone know the origin of the phrase "All's fair in love and war". Is there a literature background? thanks

ALL'S FAIR IN LOVE AND WAR -- "The rules of fair play do not apply in love and war. The proverb has been traced back to John Lyly's 'Euphues' . First attested in the United States in 'Horse-Shoe Robinson' . The proverb is found in varying forms. The proverb is frequently used to justify cheating." From Random House Dictionary of Popular Proverbs and Sayings by Gregory Y. Titelman ( Random House, N.Y., 1996).