Semites? A fair fraction of the Muslims I know are from the Balkans, West Africa, or the subcontinent. (And a certain number of the persons of Arabic descent are Christian.) Also, it is my impression that "Semitic" works pretty well as a description of a language family, not so well as a description of ethnicity.

Having said that, yes, regarding one's fellow citizens as allied would be a good thing.

(Also, how would one hallow an alliance?)