How was James M. Buchanan awarded the Noble Prize in Economics?

Name: James M. Buchanan.
Real Name: James McGill Buchanan.
Country: United States.
Date of Birth: October 03, 1919.
Died: January 09, 2013.
Education: BS from Middle Tennessee State University, MS from University of Tennessee, and Doctor of Philosophy (PhD) from University of Chicago.
Subjects Of Study: Public-choice theory.
Popularly Known: Best-known work is Calculus of Consent and his known for his work on public choice theory.
Noble Prize Year: Nobel Prize for Peace in 1986, for his development of the contractual and constitutional bases for the theory of economic and political decision-making.