"In London, Choudary and his students provided detailed descriptions of how the Islamic State must conduct its foreign policy, now that it is a caliphate. It has already taken up what Islamic law refers to as "offensive jihad," the forcible expansion into countries that are ruled by non-Muslims. "Hitherto, we were just defending ourselves," Choudary said; without a caliphate, offensive jihad is an inapplicable concept. But the waging of war to expand the caliphate is an essential duty of the caliph."