In the first add-on for Age of Empires III you continue to play the story of the Black-family. Now you begin as Nathaniel Black, son of Nonahkee - a Iroquois - as he struggles to find his place in the new world. And with the Independence War not far away the decision for whom his heart beats, doesn't get any easier. Later you take control over Chayton Black, grandson of Nathaniel who needs to take the side of the Sioux or his fellow settlers during the Black Hills Gold Rush.
The add-on adds three new playable parties to the game (Aztecs, Iroquois and Sioux) as well as several new units and buildings to the existing parties like a Spy or a Saloon.