A number of publishers have series of what are called "companions" or "handbooks." These books take a topic within a large field and provide a range of articles covering multiple aspects of that topic. We purchase many of these companions as e-books but some are only available in print. Below you'll find either a link directly to the series or links to browse through the various titles in a series through the Franklin catalog. You'll find the link to an individual e-book in the Franklin catalog.
For Persia, use Iran. The subject heading for the history of Persia is
Dictionaries and encyclopedias can be very specialized and may help you with vocabulary, names, dates, variant spellings, concepts, maps, and more.