Essentially, all of Part 2 is an answer to this question. If you look at the subtitles of all of these chapters, you will get an idea as to what Diamond says is the reason that some places get "civilized" more quickly.
Diamond is arguing that it is really a matter of geographical luck. He says that civiliation comes from farming and that some places were luckier than others because they had better chances to become agricultural.
In Part 2, he looks at how this is. He looks at things like how many kinds of plants and animals could be domesticated. He looks at how easy or difficult it was for crops to spread from one place to another. These are a couple of main examples, but there are others, because all of Part 2 is an answer to your question.