There are twenty-two factions in Medieval II: Total War. In the Grand Campaign game seventeen factions are playable. Of these, only England, France, the Holy Roman Empire, Spain, and Venice are available from outset.
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The other playable factions may be unlocked all at once by winning a campaign (short or long) as one of the five initially available factions. Alternatively, they can be unlocked, one at a time and regardless of whether the campaign is won or not, by conquering all their settlements (including occupied temporary forts) or by killing their entire royal family.