As posted in the news page,
Here is a summary of the new info:
* The new Warlord unit emerges as your civilization gains combat experience. You can use them just like other Great People to discover technologies, start golden ages, and join cities as Great Specialists. The real special ability of a Warlord though is to venture out into the field and attach themselves to military units. The units attached to these leaders gain combat advantages.
* The six new civilizations and their leaders are the Zulus (Shaka), the Celts (Brennus), the Carthaginians (Hannibal), the Vikings (Ragnar), the Ottomans (Mehmed II), and the Koreans (Wang Kon). The new civilizations have the same unique unit as in Civ3, with the exception of the Ottomans. The Ottomans's unique unit is the Janissaries (in Civ3 it was Sipahi). Rameses II is confirmed as the new leader of Egypt.
* Some of the civ-specific buildings are the American Mall, the German Assembly Plant, the Roman Forum, the Greek Odeon, the Spanish Citadel, the French Salon, the English Stock Exchange and the Aztec Sacrificial Altar.
* Vassal states is like an "asymmetric alliance." Basically, one civilization serves as the master in the relationship and collects tribute from the weaker, vassal nation. The vassal nation is automatically at war with any of the master nation's enemies. Most importantly, the vassal's land counts as the master's land for domination purposes. You can get a nation to be your vassal if you can get them to "trust you enough to protect them or if they're scared enough of your power."
