About the Vikings? Sorry, but they did come and their impact was ZERO. I am looking to find out how things would have been changed if Columbus had NOT discovered America. The best assumption is that Portugal, by far the leading nation in exploration at the time, would have been the ones to have discovered the New World.
the Vikings made little impact on the Americas, but there is (female) DNA from the Amerindians in a small number of Icelanders/Norwegians, suggesting that they might have brought some slaves back with them...