Age of Empires II: The Conquerors Expansion is the first expansion pack ever released for Age of Empires II: The Age of Kings, it featuring five new additional civilizations:
The Aztecs, Mayans, Spanish, Koreans, and Huns.
Additionally, there are 4 new campaigns, 11 new units, 26 new technologies, new gameplay modes, new maps and different minor tweaks to the gameplay. A second expansion titled Age of Empires II: The Forgotten was released in 2013. Various new gameplay features and tweaks were added, including new game modes such as: Defend the Wonder, King of the Hill and Wonder Race.
Age of Empires II: The Conquerors Expansion Screenshots:
Age of Empires II: The Conquerors system requirements: