What is the theme in When China Ruled the Seas: The Treasure Fleet of the Dragon Throne, 1405-1433 by Louise Levathes?

Major themes addressed in Levathes', When China Ruled the Seas: The Treasure Fleet of the Dragon Throne, 1405-1433, include why the early Chinese took to the seas, the impact of Confucianism on China's maritime trade, and the way in which Chinese dominance of the high seas spread Chinese culture.