I know that Niall Ferguson is a somewhat controversial historian, but I really enjoyed his book and BBC television series <em>Civilization: The West and the Rest</em>.
He talks about "6 killer apps" that made the West the civilization that conquered the rest of the world. He discusses the exploration of Zheng He, and the fact that China chose to end it's exploration program at that time. The characteristic of Western civilization that made them different, according to Ferguson, is competition. China was, and is, one of the largest land empires in the history of the world. China didn't need to explore new lands in order to consolidate it's wealth. The seafaring nations of Europe (mostly the Dutch, English, Spanish and Portuguese) were all small countries in direct competition with one another for wealth and military dominance. In that climate of competition, it was cruicial for each of the countries I listed to build overseas empires as quickly as possible.