The Age of Exploration: Chapter 9, Exercise 1 — Possible Solution
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CAUSES NAMED
Disease (smallpox, influenza, pneumonic plague), violence and enslavement
(warfare, forced removal, massacres), and social disruption that damaged food
systems and social structures.

WHY THE RANGE OF ESTIMATES MATTERS
Pre-contact estimates run from 8 million to 100 million. The size of a
decline depends on the starting figure, so the same later population implies
very different losses. The source says the debate is extensive and I did not
find how estimates are made.