islam principle is onevry where ,and according to Quraan and some hadith ,a muslim man can marry a christian or jewish girls simply coz they do beelive in same god and another point he can marry her even if she doesnt want to converT to islam and he has to respect her Worships.
AND he can mary girl whose not christian or jweish as long she beelive in same god coz this important for the sake of kids to be both parents in beelive in same god