Hence demonstrating there was at least one other key factor behind which nations/empires were able to successfully establish overseas colonies - but arguably that itself was not an "ultimate" cause that was out of the control of earlier civilizations (in the way availability of species suitable for domestication was). If the Roman empire hadn't collapsed the way it did the world would surely look very different to how it does today (I wouldn't be writing this in English for a start!). I don't think that's something Diamond addressed in GG&S, and even in Collapse I don't remember any serious discussion of how it might be ultimately and primarily due to geo-environmental factors (for a start, the empires that replaced it over the following centuries were operating in very similar ecologies/climates). I don't think Diamond would insist that the pattern of historical development of specific nation states was largely due to the ultimate causes he tries to identify for overall European hegemony, but it would be surely worth clarifying at what scales other factors start to become more important (and what those factors might be).
(Actually the far better example is France - in principle, at the time, it was better obviously placed to achieve colonial domination than Spain or The Netherlands or even Great Britain. The argument seems to be that it was too focused on waging wars within Europe itself to commit itself to overseas exploration etc. But is that an "ultimate", proximate or some sort of intermediate cause?)
