Which war saw the first official establishment of sutlers' stores that would eventually evolve into the modern military Post Exchange (PX) system?

The Army and Air Force Exchange Service (AAFES) and other military retail operations have a fascinating history that revolutionized how servicemembers accessed goods. These military retail innovations have influenced civilian retail practices and technologies. This trivia question explores the origins of formalized military retail establishments that would eventually evolve into the modern Post Exchange (PX) system we know today.

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American Civil War
World War I
Spanish-American War
Mexican-American War