It's a mangled version of Marvin Harris and Fernand Braudel.

I tried to read _Guns, Germs, and Steel_, and gave up in disgust; Jared Diamond is a Green with an axe to grind. In the case of the American Indians, geography and disease did ruin them (or rather, it ruined the North Americans and the Amazonians; Mesoamerica and the old Inca Empire are predominantly Indian to this very day, and the most recent Maya revolt against the Spanish colonists was in 1911); but most of the time -- more or less all of the time, in the Old World -- ecological factors are secondary to cultural ones. Look at the history of rice: it was adopted as the basic grain of Persia before it was adopted as the basic grain of China (and long before Japan), because good Zoroastrian piety inspired the Sassanids (IIRC) to import this miracle grain and thereby ensure the prosperity of their peasants.

I think that what's wrong with Diamond is best summarized in his book _Collapse_, the only work I have ever heard of that discusses how civilizations disintegrate and makes no reference whatsoever to Rome. His thesis is that civilizations fall due to ecological mismanagement, so he doesn't mention any that don't fall due to ecological mismanagement -- even the Roman Empire itself! (He admits in the preface that not all civilizations fall due to ecological reasons, but that suggests that the title of his book -- _Collapse: How Civilizations Choose to Fail or Succeed_ -- should have been something a lot less authoritative.)

For what I think is actually the case, look up Peter Turchin's _War and Peace and War_, an "old-fashioned" -- or rather, newfangled -- work pointing to the importance of civilizational cohesion (Ibn Khaldun's asabiya, but not the normal Arabic definition of it) in the rise and fall of civilizations. Turchin is a population biologist by training, and tried turning his modeling techniques to history -- whereupon he was astonished to discover that a simulation with one variable and about four rules accounted for pretty much the whole range of human experience. The gory, algebraic details are in _Historical Dynamics: Why States Rise and Fall_; but _War and Peace and War_ is more accessible and has more historical examples.

One other sidenote: guns and steel were not the fates of the two societies that Diamond was probably thinking of (certainly the two that came to my mind). It's a widely-held legend that Cortes and Pizarro defeated the Mexica and the Inca respectively by attacking with massive numbers of technologically-superior forces.

In reality, Cortes was the leader of a band of adventurers that never got over 2,000 men and was normally closer to 150, most of whom carried swords and crossbows (and abandoned their clumsy, hot steel cuirasses for Mesoamerican quilted-cotton armor); he had about 30 horsemen at the beginning of his campaign, and in one of his decisive early battles was down to something like 15. He didn't win by a technological advantage; he won by his personal courage, the courage of his men, an enormous amount of luck... and the fact that the Triple Alliance thought that it was a good idea to leave a small state that hated them like poison, Tlaxcala, independent -- twenty miles away from Tenochtitlan. (This meant that they could fight the Tlaxcalans to collect a lot of prisoners for sacrifice, and give their men a lot of promotions: the _Codex Mendoza_ has a table of Mexica level-ups that would embarrass Squaresoft.) A friend of mine once quipped that any civilization that thinks that _that's_ a good idea, deserves what's coming to them.

Pizarro maneuvered his way into a badly confused war of succession, imprisoned/befriended one of the two leaders, murdered him, and then pulled the same trick on the other one -- he won through politics, not through power. Even then, it took the Spanish government forty years of campaigns with regular infantry to fully conquer the Inca Empire (I've always wondered why Spain accepted Pizarro's treacherous conquest as opposed to telling him to stuff it, but his having already shipped back an entire roomful of gold bars and two roomfuls of silver may have had something to do with it)... but, again, it wasn't technology that let Pizarro win, it was politics, the same kind of thing that let the Manchus conquer China.

See _Seven Myths of the Spanish Conquest_ for details on both. You may even want to read _Our Lady of Guadalupe and the Conquest of Darkness_ -- an extremely, exuberantly partisan Catholic history of the conquest of Mexico (but still adventuresome, rousingly entertaining, and meticulously researched), which omits not a single detail except Hernan Cortes' five Mexica concubines. (Cortes was married at the time, and was a fairly serious Catholic. As a fairly serious Catholic myself, I have often tried to figure out what on Earth he thought he was doing, but have more or less given up on it.)