Several of his books focus on Iran but deal also with the larger Muslim world, including The Patricians of Nishapur: a Study in Medieval Islamic History (1972), Conversion to Islam in the Medieval Period: An Essay in Quantitative History (1979), and Islam: the View from the Edge (1994). His books on a broader view of Islamic history and society include Under Siege: Islam and Democracy (1994) and The Case for Islamo-Christian Civilization (2004). His book The Camel and the Wheel (1975) brings together his interest in the histories of technology, animal domestication, and the Middle East, dealing for example with the significant military advantage early Muslim armies gained from a slight improvement in the design of cloth camel saddles.