An investigation of how tribalism affected the evolution of the human mind. The analysis reveals a process that beliefs are a primary means of group identification and are a natural component of the evolution of human thought and culture. The results are mental processes that divide population groups into "us" and "them" which result in methods of thought and perception that affect major areas of human culture, specifically politics and religion. Us Against Them argues that the essential difference between the religious/conservative and the secular/liberal is driven by tribalism, not ideology. This is evidenced by the exclusive nature of conservative ideology that divides people into separate groups as evidenced by common features such as "you're with us or against us", "believers and heretics", and "attack to defend". The book is written for the general public without technical jargon and is arranged as a series of arguments in the manner of traditional philosophy.