The eventual decline and stagnation was the effect of the decision to close China's doors. But the cause of the end of the expeditions was largely financial. Culture also has an important role to play. The Chinese were not looking for new lands or have any interest in converting people to their religion. They were looking for respect and recognition. They want to prove to the world that China is the undisputed power on Earth and that they are the pinnacle of civilization. They could not have imagined that the world is about to enter into a period of tremendous change so they felt no reason to change their imperial system. How can you change perfection? ...LOL