Age of Empires II: The Conquerors Expansion

"Age of Empires II: The Conquerors Expansion (sometimes abbreviated to AoC or AoK: TC) is the expansion pack to the 1999 real-time strategy game Age of Empires II: The Age of Kings. The Conquerors is the fourth installment in the Age of Empires series by Microsoft Game Studios and Ensemble Studios. It features five new civilizations (the Aztecs, Mayans, Spanish, Koreans, and Huns), four new campaigns, eleven new units, twenty-six new technologies, new gameplay modes, new maps and different minor tweaks to the gameplay.
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Source: Wikipedia, "Age_of_Empires_II:_The_Conquerors," available under the CC-BY-SA License.