 It is, to be sure, contrary to the Christian Faith that anyone who is unwilling and wholly opposed to it should be compelled to adopt and observe Christianity.For this reason a valid distinction is made by some between kinds of unwilling ones and kinds of compelled ones.Thus one who is drawn to Christianity by violence, through fear and through torture, and receives the sacrament of Baptism in order to avoid loss, he (like one who comes to Baptism in dissimulation) does receive the impress of Christianity, and may be forced to observe the Christian Faith as one who expressed a conditional willingness though, absolutely speaking, he was unwilling ...

During the Northern Crusades against the pagan Balts and Slavs of northern Europe, forced conversions were a widely used tactic, which received papal sanction.