Which game is widely credited with popularizing the 'free-to-play with microtransactions' business model in Western markets that revolutionized game retail?

The gaming industry has transformed how digital products are sold through innovative retail strategies. One of the most significant retail innovations was the introduction of microtransactions and in-game purchases, which revolutionized game monetization models. This poll tests your knowledge about the origins of this retail innovation that now generates billions in revenue annually across the gaming landscape.

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League of Legends (2009)
World of Warcraft (2004)
Farmville (2009)
Team Fortress 2 (2007)