Guns, Germs and Steel

Why did Europeans conquer most of the world?

Useful wild plant species and big mammals that could be domesticated led to a significant lead in the Fertile Crescent and China compared to the rest of the world in food production. This caused:
- greater human densities, which caused more disease and thus disease resistance;
- specialized crafts people, which caused improved technology;
- specialized bureaucrats, which facilitated writing;

The rest of the world didn't have the food production and big domestic mammals on which to build powerful civilizations.
China was homogeneous and rulers put brakes on development and exploration.
Fertile crescent agriculture was not sustainable and lost it's development lead.
Europe imported food production and technology, and, driven by inner conflict, focused much more on development and exploration.

Thus when Europeans started expanding, they had far better technology and organization than everyone else, and carried a number of deadly epidemic diseases, the only barriers faced were local disease in tropical regions.

At least, this is what I understood from the book.