Minor factions are unique CPU-controlled factions that cannot be selected by players. Defeating or allying with a Minor Faction can earn a player access to its unique units and resources. Most Minor Factions are designed around a specific map - however, they are able to appear on any map.
Crisis Factions are unique, universally hostile CPU-controlled factions that can appear on maps during certain circumstances. Crisis Factions are extremely overpowered "Boss" factions that require extremely powerful player factions or the cooperation of multiple players to defeat.