Perhaps, but following their legendary voyage over the Pacific, China rapidly sealed off its frontiers to the outside world and isolated its dominion. Because no foreigner was able to make significant advances into conquering the Americas until the introduction of Tiny Pox, 1500s, the Native Americans would have been more than capable of repelling any assault by a small fleet of Chinese ships. If it weren't for the pandemics that killed off the Native Americans during the Spanish and Portuguese invasions, they would have fiercely fought any intrusion.