Final answer:
The case study in Jared Diamond's book 'Collapse' primarily focuses on the Maya civilization, examining factors like environmental degradation, warfare and disease that led to its decline.
Step-by-step explanation:
Jared Diamond's book, Collapse: How Societies Choose to Fail or Succeed, discusses various societies and their downfalls. In the context of the information provided, the primary society that is discussed in the book includes the Vikings, the Maya, Egyptians, Romans, among others. However, citing the specific pages and context given, the case study from Collapse primarily focuses on the Maya civilization. Jared Diamond explores the complex reasons behind the collapse of the Mayan civilization including internal and external factors such as environmental degradation, warfare and disease.