There was one novel called Kalvan somethingorother, that suggested a huge migration of IE peoples going north, over to Alaska, and down into North America. Gunpowder was discovered too.
Lord Kalvin of Otherwhen - H. Beam Piper, first AH novel I ever read, and started a lifetime fascination with the subject.
There are something like fifty AH stories of his over on Project Gutenburg, I highly recommend them.
Many of the stories in the Paratime series are going to seem familiar, since the terminology he invented pretty much defined the genre.
Basically, Lord Kalvin is Calvin Morrison, a PA state trooper who gets ISOT into another world, where the Indo European migrations head across the Bering Land Bridge. In this TLs equivalent of 1964, the East Coast is Five Pan-theistic Kingdoms of OTL Thirty Years War technology. Gunpowder is a monopoly of the House of Styphon...between gunpowder and moneylending, Styphonism is trying to become a monotheism and drive out worship of the other gods. Calvin, a history buff, DOES know the gunpowder recipe, and winds up, thorough a couple of lucky breaks, winds up running what turns into a wank.
The Overview of this is the Paratime Secret - which sounds kind of ASB when you view it from the outside, but makes sense when you read it through.
Humans on earth are the descendents of colonizers from 100K years ago. 50,000 years ago, one TL found out how to cross TLs. They found what Piper called five "Levels" - TL Zero is their world. First Level is where the colonization was sucessful. Level two is where colonization was sort of successful, but they had a lot of trouble, and some Dark Ages. Level Three is where the colonization had a lot of trouble. Level Four (our TL is in this area) -the Colonization ran into a LOT of trouble, a LONG dark Age followed, and the humans think they evolved on Earth. Fifth Level are earths where no humanity ever took hold.
I really recommend you look these stories up, if you like AH - Piper is probably, the first and one of the best AH writers of all time. Sure, his stories often seem a bit dated and hoky - they were, after all, written in the late fifties and early sixties, many published after his suicide.