I agree with the other responses, and would also point out that a history of religion, especially a cultural history of religion, reveals a great deal that an institutional history of a church might overlook. What interests me more than the history of popes and priests (though these are very interesting and legitimate topics for study) is the study of popular belief and religious practice. In many cases, there is a large gap between what the church teaches and what individuals often believe. There are deep cultural, social, economic, and other factors that have implications for human belief. There is actually a very large historiography of both church history and popular belief, in Europe and the Americas. I suspect the same is true of other places as well.