This is the standalone expansion to Civilization IV and it doesn't require the base game in order to run.

Sid Meier's Civilization IV: Colonization is the third offering in the award winning Civilization IV series. A re-imagining of the classic Colonization game Sid Meier created in 1994, Sid Meier's Civilization IV: Colonization is a total conversion of the Civilization IV engine into a game experience in which players will lead a European nation on their quest to colonize and thrive in the New World. Players will be challenged to guide their people from the oppressive motherland, discover a New World, negotiate, trade and fight as they acquire great power and battle for their freedom and independence.

Features:

• Classic Game Design Rebuilt for the Modern Era: Usher forth a new generation of Sid Meier's Colonization gameplay built on the award-winning Civilization IV engine, providing the beautiful visuals, famously addictive gameplay and endless fun that are synonymous with Sid Meier strategy games.
• Fight the Homeland and Establish a New Nation: Play as the English, Spanish, French or the Dutch and journey to a brave new world in search of freedom from your oppressive homeland.
• Improved Diplomacy: Sustain peace and support your followers as you engage in advanced negotiations with natives, other colonists and the hostile homeland - Trade resources, gold and land as you build the foundation for a self-sufficient and powerful colony.
• Historical Figures Provide Adaptive Gameplay: Acquire founding fathers such as John Smith, Patrick Henry and Samuel Adams who will help guide your nation to freedom based on your gameplay style.
• Brand New Interface: Both Civilization IV fans and players new to the series will feel right at home with an interface that Firaxis has built to be accessible and easy to navigate.
• Multiplayer Offers Endless Replay Value: Compete with friends from all over the world via the Internet and Play by Email modes or compete locally via the Hotseat and LAN modes, offering endless ways to conquer the New World.
• Mods & Community Tools: Players will have limitless options for modifying the game to suit their needs. Firaxis will ship the game with modding tools including a map editor using XML and Python.