I would start with solid, well researched history. Maybe the books of Karen Armstrong, who is quite strong in comparative religion.

I would suggest to read History concerning the Reformation, The Dark Ages and Inquisition. Your belief is your disbelief that can be reached by examining the wars, torture and bloodshed which were spurred and ignited through anyone who dared confront or question. Lost Scriptures by Bart Erhman, 'Here I Stand' by Roland Bainton. You will find all the necessary suggestions about beliefs and how they got started. Don't forget to look up Erasamus, Jan Hus and John Wycliffe. Just make sure that you get documented and renown Scholars and Academics whom have no Religious Affiliations whatsoever. Try it you'll be on the road to what you are pursuing.

Any science text book might be a good place to start.

A Separate Reality

Where the red fern grows

the bible.

Drunk With Blood: God’s killings in the Bible by Steve Wells is informative and funny.

If you don't mind me asking.. What do you mean by "our beliefs"? Being an Atheist = lacking of a belief or rejection of supernatural claims.. A-THEISM = Not a theist.. Agnosticism= lacking of knowledge of supernatural claims.. You can be a Humanist, secular or otherwise, a skeptic,. Etc..
But if you are looking for a good read... ' Letter to a Christian Nation' Sam Harris.. is a very easy but powerful read.. also 'The End of Faith' also by Sam Harris.. of course 'The God Delusion' , Blind Watchmaker, Selfish Gene, by Richard Dawkins and 'god is not Great how religion poisons everything', Hitch 22.. 'Foundational falsehoods of Creationism' Aron Ra.. and Dr. Richard Carrier's books on the historicity of Jesus..
Hope that helps

Why I Am Not A Christian, Bertrand Russell.