Sega announces Empire: Total War - The Warpath Campaign, an add-on for Empire: Total War (which is required to play the expansion) that will be released next month via Valve's Steam service, where pre-purchases are already being accepted. The announcement includes screenshots, a gameplay trailer, and the following rundown:

The Warpath Campaign Expansion is only available through Steam. Check the Downloadable Content page on Steam to purchase and unlock the new campaign and all 5 new American Indian factions. These factions can be played in single player and multiplayer games.

A new detailed North American Campaign Map expands the Empire: Total War experience, with 5 brand new American Indian factions, new units and technologies. Experience battles in the new Warpath Campaign and lead one of the 5 new factions in an epic war to defend your lands and drive out the invaders. Or take these units and their unique strengths into multiplayer battles.