The best place to find the answer to this question is in Figure 4.1. There, Diamond shows us what he sees as the ultimate factors that led to the proximate factors that have allowed Europeans to have (as Yali pointed out) so much wealth and power.
There are two or three ultimate factors (depending on how you count them), both of which are geographical. First, there is the presence (or absence) of many wild species of plants and animals that could be domesticated. Second, there is the ease (or lack thereof) of species spreading, which is caused largely by the length of a continent or region's east-west axis. These are the most basic factors that determine, according to Diamond, which societies have become rich and powerful and which have not.