View the 4-part series by Youtube's Extra History channel on early Christian Schisms to improve your understanding of the basic background. Keep in mind, the creators are not subject-matter-experts, but they do a good enough job introducing you to the foundational concepts in an entertaining way.
The Oxford Illustrated History of Christianity by 
Provides a deep survey of more than 50 past and present religions practiced throughout the world. Includes thousands of primary and secondary sources that examine core beliefs, customs and practices, celebrations, key events, sacred places, and significant figures.
Search for your relevant theological terms and look for results tagged as "Peer Reviewed | Academic Journal" or filter the results by choosing the "Source Type" as "Academic Journal."
