I believe that the answer to this is to be found on p. 21 of the book (this is according to Amazon’s search function. I do not know what version of the book this is. Mine is on Kindle and therefore has no page numbers). It can be found under the heading “The Three Forces.” Zakaria is arguing that changes in these three forces have shaped the world since the Cold War. The forces are politics, economics, and technology.
Zakaria’s political force is the end of communism. During the Cold War, it was still plausible to some degree to think that communism might be the correct way to run a country. If not, there could at least be a semi-socialist “third way” such as that taken by India. With the end of the Cold War, this idea was disproven and it was clear that democracy and capitalism were superior.
The economic force that Zakaria is talking about is very similar. Basically, he is saying that liberalization of economic policies created a time of unparalleled growth and stability. He is saying that countries adopted sound monetary policies (thus defeating inflation) and allowed capital to move around the world freely. He argues that this has made the world much more economically stable and prosperous.
Finally, Zakaria cites technology. Specifically, he is talking about communications technology. He cites Thomas Friedman’s idea that this technology has made the world “flat” and he agrees with Friedman that this is a very important development.
Thus, the three factors are changes in politics, economics, and technology.