Well, let me tell you this.

I have a wonderful book, thick as a Bible, and written very, very well. A wonderful read, if only I had thei time and the will to go through it all.

The title is "1421, the year the Chinese discovered America" and explains how a certain Chinese Emperor sent a HUGE fleet of HUGE ships to map the entire Indian and Pacific Ocean.

It seems this fleet explored and mapped the entire west coast of both North and South America.

Unfortunately, by the time the fleet returned home after over 20 years, the old Emperor had died and the new Emperor was after the adage "I am who I am, and the rest of the world is neglectable"
meaning "What's inside China is the world, the rest are impure non-chinese".

Else, by the time Cortes and Pizarro arrived, they would have found a very efficient and extremely aggressive chinese military to defend "Imperial interests in the New World".

Who knows... maybe the Maya and the Inca and the Aztects would have survived..   and the American Indians west of the Mississippi...