One of my favourite TLs is the BANW, which began by giving the Arawaks a more advanced navigational package. I was thinking about other possibilities for a neolithic naval expansion having effects around the world. One possibility I thought was the Ainu.
The Ainu, natives to Japan, the Kuril Islands and Sakhalin, are already considered to be related to Amerindians by some scholars. I was thinking about if the Jomon (proto-Ainu) had a better navigational package and more of a naval bent, expanding a single cultural-linguistic community from northern Japan in the East to the Aleutians in the west. As time goes by, I could see them making their way along the Alaskan coastline, displacing locals.
I see it as happening slowly at first, but after 1200 as Ainu are more aggressively displaced by the Japanese moving north they flee enmass to the Aleutians, Alaska or the Pacific Northwest.
What interests me is how this vector could have facilitated the transmission of Eurasian diseases, animals and technology to the New World by way of Ainu exploration, trade and settlement. Assuming a long term period of low intensity interaction followed by increasing intensity as the Japanese displace the Ainu from their traditional lands it could allow part of the Columbian exchange to occur early.
There may be awareness of the New World on the part of East Asian societies, particularly in stories of vast and rich fisheries. This may attract Japanese and Koreans to follow the Ainu trade routes and further facilitate the interactions.
It would mean that some of the Eurasian epidemics in the New World would be introduced early, it could see the early introduction of the horse and ox (both part of Ainu traditional cuisine) to the New World. The technological gap between the Amerindians and the Ainu would be easier to close and they would have more affinity than with the Europeans. If the Japanese, Koreans or Chinese explore the Ainu trade routes attracted by the chilli or chocolate trade then the Americas could become the western edge of the great Asian trading system. Which would change things even more significantly when and if Europeans arrived.