Which wartime innovation first established the modern military PX (Post Exchange) system that revolutionized how the U.S. military approached retail operations for troops?

The military exchange system (PX/BX) represents one of history's most unique retail innovations, combining customer loyalty and service member support. These facilities have evolved from simple sutler wagons following troops in the 1800s to sophisticated retail operations serving millions worldwide. Beyond convenience, they've pioneered retail innovations that later spread to civilian markets and created a distinctive shopping culture that spans generations of military families. Test your knowledge about this fascinating intersection of military history and retail development!

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The Civil War's sutler system that followed Union Army regiments
World War I's establishment of standardized exchanges at training camps
The Revolutionary War's commissary wagons for Continental soldiers
World War II's introduction of tax-free purchasing for deployed personnel