Which wartime retail innovation first established the modern military Post Exchange (PX) system that dramatically improved soldier retention and morale?

Throughout military history, the way soldiers accessed goods has evolved significantly. The Post Exchange (PX) system represents one of the most successful retail customer retention strategies in history, keeping military personnel supplied with necessities and comforts across global deployments. This poll tests your knowledge of this unique retail system that bridges military operations and consumer commerce, and how it revolutionized brand loyalty and customer experience for service members.

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The Civil War's Sutler system, where civilian merchants were licensed to follow armies and sell goods
The Spanish-American War's canteen system, which established the first official military-run retail stores in 1895
World War I's Liberty Stores, created in 1917 to provide American products to overseas troops
World War II's Ship's Service stores, which pioneered the tax-free pricing model for deployed personnel