I have read several good reviews about A History of Christianity: The First Three Thousand Years by Diarmaid MacCulloch (NY Times, The Guardian). It appears to be a very comprehensive look at Christianity's history and impact on society.
About A History of Christianity:
Christianity, one of the world’s great religions, has had an incalculable impact on human history. This book, now the most comprehensive and up to date single volume work in English, describes not only the main ideas and personalities of Christian history, its organization and spirituality, but how it has changed politics, sex, and human society. Diarmaid MacCulloch ranges from Palestine in the first century to India in the third, from Damascus to China in the seventh century and from San Francisco to Korea in the twentieth. He is one of the most widely traveled of Christian historians and conveys a sense of place as arrestingly as he does the power of ideas. He presents the development of Christian history differently from any of his predecessors. He shows how, after a semblance of unity in its earliest centuries, the Christian church divided during the next 1400 years into three increasingly distanced parts, of which the western Church was by no means always the most important: he observes that at the end of the first eight centuries of Christian history, Baghdad might have seemed a more likely capital for worldwide Christianity than Rome. This is the first truly global history of Christianity.