As the latest chapter in the best-selling real-time strategy series, Age of Empires III explored the age of colonialism when European powers settled the Americas, and then fought it out with one another. You take command of any of the major powers and attempt to conquer the New World the old-fashioned way by collecting resources, constructing buildings, and raising armies. Microsoft and Ensemble will explore this era further with Age of Empires III: The WarChiefs, the upcoming expansion pack that not only adds in new content for the existing European civilizations, but also lets you play as the Native Americans for the first time. For the latest details, we caught up with lead designer Sandy Petersen, and he filled us in on some interesting new features. Some might even call them "revolutionary." The WarChiefs is scheduled for release later this year.

The WarChiefs expansion adds a considerable amount of content to Age of Empires III.

GameSpot: We understand that the new WarChief unit is both an explorer and a fighting unit, based on a real-world historical figure. How many WarChiefs does each Native American tribe get, and how were they chosen? We know that the WarChief unit stems partly from the feeling that the European explorers in Age of Empires III quickly became obsolete over the course of the game, so what abilities does this new unit possess, and how will they add to the game?

Sandy Petersen: Each tribe gets only a single WarChief, and while they are based on the actions of famous historical figures, the WarChief unit itself, like the European explorers, can be named by the players. We do have historical personalities for the various natives of course, as we did with the Europeans. Each nation's WarChief has a sort of leadership effect, like an aura, which boosts all nearby units in a manner specific to that nation. The Sioux WarChief, for instance, increases nearby units' speed. WarChiefs also have other special abilities, which are highly useful. Early in the game they have the nature friendship ability, which lets them tame treasure guardians, such as bears, wolves, or even outlaws. The native nations have technologies and tribal council shipments to further boost the WarChief.

GS: Native American factions don't have home cities like European civilizations, but they do have tribal councils. What are the differences between cities and tribal councils? How are councils limited, and what unique abilities do they possess that cities don't?

SP: Tribal councils function quite similarly to cities, though, of course, they have very different shipments. For instance, the Sioux can send herds of buffalo for their hunters. The Iroquois have special combination shipments based on each of the six Iroquois nations. For example, the Onondaga nation ships tomahawk warriors along with crates of wood.

GS: Tell us about the five new minor Native American tribes in the game. We understand that one of them is the Klamath from the Pacific Northwest, but who are the others? Are they treated like Native American tribes were treated in the core game, in that they're basically outposts with which you can set up trading posts and unit recruitment points?

SP: The minor tribes are treated exactly as the existing Native Americans in Age of Empires III. Not all of the minor tribes have been announced yet, but two that I'd like to mention are the Cheyenne and the Huron.

GS: Aside from covering a different area in the western half of the Americas, what are some of the differences in WarChiefs' maps from those of the original game? Are they bigger, more complex, and/or more detailed? How many new maps will the expansion offer?

The tribal council will ship you care packages of a sort.

SP: We have quite a few new maps in the expansion. In each case, we've tried to add some new interesting strategic feature. The Andes map has a large cluster of native settlements at one end that can add great power to the conqueror. The Northwest Territory map is interesting in that most of the action takes place on the mainland, but there is a large island off the coast that can support a large base, so players who "go navy" might be able to parlay this into an advantage.

GS: The existing European civilizations will each receive new content. What sorts of additions are being made, and how will they change the game? What's your favorite new European content and why?

SP: The Europeans are getting an enormous amount of new material. There is a special new feature for European civs only. It is a new way to win the game and we're very excited about it. Revolution is an alternative to the game's Imperial Age. If you are in the fourth age and are a European nation, you can spend resources to research the revolution. When you do so, you get to choose from two different historical New World revolutionaries, such as Simon Bolivar, Toussaint Louverture, or Father Hidalgo. Each revolutionary hero provides a different advantage.

When your revolution is complete, your flag changes to a new one, your home city is replaced with a revolutionary city (with new shipments!), and all of your settlers transform into colonial militia. For the rest of the game, you can no longer train settlers, and your economy basically slides to a standstill. However, your military power is enormous. Once one side revolts, the other side, by definition, become the imperialists and can't revolt.