Perhaps see
1421exposed to see what credible historians think of Gavin Menzies fantastic history of the world.
It's only fair the author's own website:
1434 Gavin Menzies | 1421 | Chinese Voyages | Renaissance history |medieval history | maritime exploration |Chinese Exploration | Admiral Zheng He | Chinese Junks
Wikipedia trashes him lavishly for not speaking Chinese, ramming a US minesweeper when in command of HMS Rorqual and lying about the routes he sailed.
Somehow this helps prove that Admiral Zheng He's fleets did not circumnavigate the globe, I guess.
Although you can dig it up under "Discussion", the Wiki frontyard entry also omits that he served on HMS Resolution, a Polaris submarine. Um my guess is that the RN screens for reckless liars when assigning folks to duties involving nuclear weapons, so I'd say he was sane. Or at least he didn't let politicians do a whale jump with his submarine and sink a Japanese trawler over half a century after the end of World War II!
I see three reasons that "professional" or "credible" historians come down hard on Menzies (1) He lays down the evidence like a story teller rather than an academic versed in the norms of academic literature (2) His evidence requires a complete rethink of world history, viz Zheng He pioneered most of the world's trading ports and distributed world maps, followed by a period of Chinese isolationism, which allowed Britain, Portugal and Spain to expand as rapidly as they did, and (3) Christianity loses lots of points because
Christopher Columbus was on God's mission and the Renaissance has been sold as a very Christian achievement.
By the way, some nitpicker researched the names of Columbus' three vessels Nina, Pinta and Santa Maria. There was indeed a Nina and a Pinta but the closest match to any Santa Maria was the Maria Galante.
All three names would inspire any sex-starved sailor: La Maria Galante = The Gallant Maria in the sense of a lady who obliges anyone's every wish; La Pinta = The Painted (Woman) in the sense of a sidewalk sex worker; and La Nina = The Cute Little (Woman). Addiion of "woman" is justified by "La", which is the feminine pronoun.
The shift from Maria Galante to Santa Maria traces back to Columbus' spin doctoring.