Faire changer de religion au vaincu

[Emp_Palpatine]

Voilà ce que dit EU2 wiki:

Force-Conversion : costs 50% warscore, and it must be asked in a separate peace. Force-Conversion may only be enacted between : a) western-rite Christians (CRC/Catholic vs. Protestant/Reformed), b) Muslims (Shiite vs. Sunni), and c) anyone may FC pagans. Western-rite Christians may change back, and will probably do so if they have more provinces of their old religion, but may only do so after the expiry of the truce. Muslims and pagans cannot revert to their old religion, due to the impossibility to convert from Sunni to Shiite (and vice versa) or to paganism.

Donc, tu dois être chrétien (évidement pas de la même religion que l'ennemi), le faire dans une paix séparé.