
Crosby argues that the expansion of European culture and genetic stock was a function of ecology and biology over time rather than a result of quick and painful conquests.
The longer answer involves the above, plus a lot of population demography and source analysis regarding the effects of "virgin soil" epidemics. Crosby's Ecological Imperialism is an excellent guide to that stuff. Even the very earliest European accounts of populations in the interior, like the expedition of de Soto, [1] are describing the aftermath of massive depopulation, since many diseases were spread by an advance guard of European domesticated animals before any Europeans actually showed up on the scene (or at least, any literate ones did).
[1] https://www.neh.gov/humanities/2004/septemberoctober/feature...
I also remember loving John Brewer's "The Pleasures of the Imagination: English Culture in the 18th Century" and Mario Biagioli's "Galileo Courtier." Also "Mad Blood Stirring" by Edward Muir, which tackles the question of why 16th century Italian street life was so incredibly violent.
Edit: seems apropos to mention that a couple friends of mine are about to launch a site for historians to curate lists of their favorite books on key topics, called Backlist: http://backlist.cc
A personal pet peeve of mine is that Alfred Crosby wrote about this stuff in the 1970s (The Columbian Exchange) and the 1980s (Ecological Imperialism) but Diamond gets all the credit for it because he successfully repackaged it for more popular audiences, without adding much.