For the first expansion to its well-reviewed turn-based strategy game, Firaxis is adding many of the things Civ fans normally expect from extended content -- including 27 new units, 14 new buildings, and 9 new civilizations (including the Celts, Mayans, Byzantines, Dutch, and Carthaginians). But the changes that have me the most excited are the re-introduction of religion and espionage to the political mechanizations.

Rather than recycle the religion system used in Civilization IV, for Gods & Kings lead designer Ed Beach wanted to build a new system from the ground up. The result is a new resource, faith, that players gather just like they do with culture and science. Early in the Grand Campaign, players have the option from choosing between the 11 most common real-world religions or creating and naming their own belief system. By choosing two values, players earn specific bonuses unique to their young religion. Players can hasten the spread of their value system by purchasable missionaries and the grand prophet moving him into new cities.

If enough people in another civilization adopt your beliefs, it will be much easier to create allegiances.Though religious influence plays a large diplomatic roll in the early historical eras, Beach says it gradually loses its importance as you advance into modern times.

If you're having problems with a rival neighbor but don't want to start a war, you can weaken their position by embedding a spy in their city. In Gods & Kings, these sleeper agents can perform impressive feats beyond just nicking technology. Rival leaders can be severely compromised by fixing elections or trying to instigate a coup with a high level agent. Make sure the risk is worth the reward before acting, though, because if your spy fails he will be executed and your relations with the country that caught him will be in tatters. Spies will also report on faction activities like troop movement, which may give you insight into whether or not the faction is saying one thing to you while doing the opposite.

Firaxis also made some significant changes to the combat system to make it more engaging. The dev team raised the hit points from 10 to 100, which means some battles will last longer than a turn. This should help players who are caught off guard to call in reinforcements to repel an unforeseen threat. In addition, they split naval units into two categories -- melee and ranged -- to give sailors more tactical options on the high seas. Melee units can raid and even capture coastal cities.

All these changes have me excited to check out Gods & Kings when it ships later this spring.