You're talking like its some kind of accepted fact that the Chinese explored the Americas, when in fact it is nothing more than a wild theory. Sure, many of the ships in Zheng He's fleet had the capability of crossing to the Americas, but you'd think if they had gone all the way over there they would have left something behind, brought something back with them (They brought tons (literally) of stuff back from all over India and Africa, but no Incan artifacts? Please!) or at least mentioned the trip in any of their journals. But no, there are no artifacts or primary or secondary sources to validate this theory. Which is why the vast majority of historians reject it. It makes for good fictional reading though...
"Examination of the book's central claims reveals they are uniformly without substance."
-Professional Historian Robert Finlay on Gavin Menzies' 1421: The Year China Discovered America
"1421: The Year China Discovered the World, is a work of sheer fiction presented as revisionist history. Not a single document or artifact has been found to support his new claims on the supposed Ming naval expeditions beyond Africa...Menzies' numerous claims and the hundreds of pieces of "evidence" he has assembled have been thoroughly and entirely discredited by historians, maritime experts and oceanographers from China, the U.S., Europe and elsewhere."
-Professor SU Ming Yang of the United States, Dr. Jin Guo-Ping of Portugal, Captain Philip Rivers of Malaysia, Captain Malhão Pereira and Dr Geoff Wade of Singapore, in a message to the Library of Congress