Between the years 1405 and 1433, a Chinese admiral named Zheng He, the "Admiral of the Western Seas," led seven expeditions from China; with him was a fleet with ships so numerous the world would not see anything like it until the 20th century.
Emperor Yongle of the Ming Dynasty, who ordered the construction of the ships, had this idea that building such immense fleet and unleashing them to the 15th century world would establish Chinese presence, impose the empire’s control over trade among nations in the Indian Ocean, and collect tribute from the “barbarians from beyond the seas”.
Well, the fleet did that, but the tribute-collecting was but for a short time, and on countries that were not exactly known for their naval power—at least not during that point in history. The fleet was undeniably huge, and could have posed as a serious threat to any country in the world, or even defeated any navy Europe could throw at it.
The Chinese armada included 300 ships carrying almost 30,000 sailors; moreover, the ships in the fleet had a design that was much more advanced than what the Europeans were using at the time. Some of the ships in Zheng He’s fleet even measured 400 feet in length!
In comparison, Christopher Columbus’ biggest ship in 1492 was only 85 feet long, while Ferdinand Magellan’s ships in 1521 were only around 100 feet long.
With this fleet, the Chinese reached East Africa, where they traded for ivory, medicine, spices, exotic woods, and even specimens of wildlife native to Africa. The fleet also visited other places in Asia, like Arabia, India, Indonesia, Thailand (then known as Siam), and other places in Southeast Asia.
The Chinese armada could easily have reached Europe and established a foot hold on that continent, and could have conquered any nation that defied Admiral Zheng He’s fleet. Had this fleet conquered Europe, world history would have been very, very different.
The Ming Dynasty emperors who succeeded Emperor Yongle, however, did not pursue a vigorous colonial policy. China, or the “Middle Kingdom,” was then deemed by its philosophers and scholars so advanced and prosperous that “barbarian nations,” who were seen as backward and poor, could not possibly add anything of value to it. Moreover, in the Confucian worldview, it was improper to go abroad while one’s parents were still alive.
The death of Emperor Yongle in 1424 signaled the end of China’s navy. Officials who encouraged Yongle’s plans of conquest by sea found themselves without a patron. Conservative scholars, whose views were rigidly Confucian and Sinocentric, dominated China’s imperial court. With the Emperor’s death, China’s age of exploration ended. The admiral himself died in 1433, during one of his voyages.
By 1500, conservative Chinese officials who did not agree with the Emperor Yongle’s dream of conquest had made it a crime to build ocean-going ships, and ordered the destruction of existing ones. They also had the blueprints for building large ships, and the records of the admiral's voyages, destroyed, just to be sure.
So ended the greatest navy in history, not in battle, as one might expect, but in the imperial court of the Middle Kingdom. Officials of the imperial court closed off China to the rest of the world.
The next several hundred years in the country’s history would prove that this decision was a very bad idea.
You can read more about the admiral, who was incidentally a eunuch and a Muslim, here.