In the early 15ht century the Ming Dynasty China was changing. they left behind their mongol ways and focused on Confucian learning. Their government became much more centralized and it was said that China was the "best governed and most prosperous" civilization of that era.
In Europe the same type of changes were occurring this time period was referred to as the renaissance. Zheung He led many voyages, but after the emperor died the voyages stopped, there was no support from other political leaders at that time. The stop of the voyages was the extinction of the best navy and stopped the potential of the grab civilization. Chinese expeditions were larger than any that Europe had ever put out. Europe sought wealth and power and possible Christianity conversions, China didn't need those things and didn't seek that through its expedition. Why Zheung He is forgotten could be because his expeditions had less potential and drive, thus making them less memorable.
n the Americas the 15th century civilizations were the Aztecs and the Incas. The Aztecs had a worldly approach they valued the world, sun and everything that is life. incas were similar but when they took over a place they wanted those who had been taken per to almost worship them. many of theses places had connections with each other amazingly.