Which wartime retail innovation first introduced the modern military Post Exchange (PX) system that revolutionized how troops accessed consumer goods?

Post Exchanges (PX) and Base Exchanges (BX) have been vital retail institutions serving military personnel for generations. These unique retail environments have evolved from simple sutler wagons following troops to modern department store-like facilities. Test your knowledge about how these military retail innovations have shaped soldier experiences and military culture throughout history!

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The Civil War 'Sutler' system that allowed authorized merchants to sell goods to Union soldiers
The Spanish-American War canteen system established in 1895, which created the first official military-run retail stores
World War I 'Victory Stores' implemented by General Pershing for American Expeditionary Forces
World War II 'Service Centers' established by the USO for troops stationed abroad