Quotes from book
Collapse: How Societies Choose to Fail or Succeed
Collapse: How Societies Choose to Fail or Succeed is a 2005 book by academic and popular science author Jared Diamond, in which the author first defines collapse: "a drastic decrease in human population size and/or political/economic/social complexity, over a considerable area, for an extended time." He then reviews the causes of historical and pre-historical instances of societal collapse—particularly those involving significant influences from environmental changes, the effects of climate change, hostile neighbors, trade partners, and the society's response to the foregoing four challenges—and considers the success or failure different societies have had in coping with such threats.

“Remember that impact is the product of two factors: population multiplied times impact per person.”
Source: Collapse: How Societies Choose to Fail or Succeed (2005), Chapter "The world as a polder: what does it all mean to us today?", section "Reasons for hope" (Penguin Books, 2011, page 524, ISBN 978-0-241-95868-1.