Answer:
Conquest.
Step-by-step explanation:
The early period of China's naval expansion could be tracked back to the Wu empire. At that time, the military's leaders at Wu notice that other territories did not posses the knowledge to properly defend military's attack from the Sea. This will made them vulnerable and made it easier for Wu to take control over their territory.
As the time progress, Chinese people started to realize that war is not only the thing that sea transportation is good for. They started to use it to find trade routes and created trading relationships with other empires.