William Dalrymple started off as a writer of travel books. He then branched off into Indian history after a trip to India aroused his senses into the rich history of Mughal and British Raj history.
He is arguably the best living English historian on this era. His books are grounded on deep and thorough research of colonial and local records. He writes well.
For his Return of a King he went deep into Afghan records in Urdu and Persian. I don’t think he knows either, but he has good researchers and translators working for him.
His Last Mughal was touted by him to be the first of his quartet on Mughal history, written backwards. {see p 72 The Sun Herald Dec 3, 2006}. I am not sure whether he has delivered on this quartet.
His latest book to be out soon is a history of how India spread Buddhism to China, Sanskrit and Hinduism to South East Asia and math’s and numerical system to the West.