Conversation so far:
When did Roberto's academic career begin?
The beginning of Unger's academic career began with the books Knowledge and Politics and Law in Modern Society.
What year did this happen?
published in 1975 and 1976 respectively.
Did the books help his career?
These works led to the co-founding of Critical Legal Studies (CLS) with Duncan Kennedy and Morton Horwitz.
What happened next in his career?
Throughout much of the 1980s, Unger worked on his magnum opus, Politics.

Question: What kind of book was this?
Self-contained rewrite: What kind of book was Roberto Mangabeira Unger's magnum opus, Politics?