The Indo-European expansions seem to have relied quite a lot on horses, wheels and chariots. To get to the Americas, you need ships, sails and navigation. I suppose you could get a more maritime Bell Beaker tradition, increasing trade between Iberian and the British Isles, eventually discovering Iceland and moving on from there.
Alternativly, the easternmost known Indo-European were the Afanasievo who just about got into Mongolia. Given the distance they had already spread, I could see them continue down to the Amur and on to Sakhalin and Japan. From which a maritime raiding tradition could develop.
I suppose there is some possibility that the Indo-European expansion could have pushed some of the Old Europe agriculturalist groups west. Megalith-builders in America.
Alternativly, the easternmost known Indo-European were the Afanasievo who just about got into Mongolia. Given the distance they had already spread, I could see them continue down to the Amur and on to Sakhalin and Japan. From which a maritime raiding tradition could develop.
I suppose there is some possibility that the Indo-European expansion could have pushed some of the Old Europe agriculturalist groups west. Megalith-builders in America.