In fourteen hundred and twenty-one
Zheng He sailed the ocean grey.
...or did he?
The 1421 hypothesis is, unfortunately, bad archaeology. I really liked the idea that the Chinese had discovered America, but unfortunately, it has been decisively debunked and appears to be wrong. The various structures which are claimed to be of Chinese origin are apparently not; and documents in the book are frequently mis-dated and have novel interpretations put on them. It was a really nice idea, but sadly not.
Author Gavin Menzies claims that the Chinese discovered America in 1421. The book seemed quite convincing, but other historians have since comprehensively demolished it, apparently. The wrongitude of his claims is more apparent in his latest effort, 1434, in which he claims that a Chinese ship landing in Tuscany sparked off the Renaissance. That is obviously wrong, because the Renaissance was sparked off by the rediscovery of classical texts and the introduction of inventions from the Islamic world and perhaps by other more internal trends. Besides, it seems unlikely that such a nebulous and widespread phenomenon as the Renaissance could have been triggered off by a single contact, even if it did actually take place.