The merchant republic government type, however, is playable with The Republic expansion. These include theocracies (such as The Papacy), holy orders, mercenaries, and republics. While the player can choose to play as any noble with at least a county in their possession, there are some government types that are unplayable without modding the game. Such a trade-off can occur in the reverse as well: one possible spouse could possess highly desirable traits but yield no new alliances for the player's dynasty. This requires balancing sometimes conflicting interests for example, while one possible marriage might allow some desirable alliance to be formed with another ruler, it may also require marrying a spouse with some undesirable traits. This adds an additional layer of strategy to marriages, such that a player will attempt not only to form beneficial alliances, but also to select marriage partners with strong heritable traits to maximise the quality of offspring and thus strengthen the dynasty. The game employs a genetics and education system, through which children inherit many traits, culture, religion and skills from their parents and guardians. The game ends when the player's current character dies without an heir of the same dynasty to succeed him/her, when all landed titles of the count rank or above are stripped from all members of the player's dynasty (including themselves), or when the game reaches its end in 1453 (unless the player is in 'observer mode', at which point the game will continue onwards).

The only in-game objective is to obtain as many prestige and piety points as possible in order to surpass the various historically relevant European dynasties in a fictional prestige ranking system (the three most prestigious ones being the Capetian, the Rurikid and the Habsburg dynasties). The game depicts or mentions numerous historical figures, including William the Conqueror, Charlemagne, Genghis Khan, Harold Godwinson, Robert Guiscard, Robert the Bruce, Harald Hardrada, El Cid, Constantine X Doukas, Harun al-Rashid, Alexios I Komnenos, Richard the Lionheart, Ivar the Boneless, Alfred the Great, Baldwin I of Jerusalem, Boleslaw the Bold and Saladin, but allows for the player to choose less-significant figures such as minor dukes and counts, and for the creation of entirely new characters with the use of the Ruler Designer DLC. Through the strategic use of war, marriages and assassinations, among many other things, the player works to achieve success for their dynasty. Players are able to start at any date between January 1, 1066, and December 31, 1337, though the Old Gods and Charlemagne DLCs allow for earlier start dates of 867 and 769 respectively, and the Iron Century update allows a start in the year 936. The game is a dynasty simulator in which the player controls a medieval dynasty from 1066 to 1452.

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