Christopher Columbus's arrival in the New World had a much greater impact that of the vikings. It was after him that the other European powers began to send over more explorers, and the subsequent wars, collonialism, etc. were all directly derived from his discovery. By contrast, the vikings only left a small settlement that was extinct within a few hundred years, and most other Europeans (indeed probably most vikings) didn't know about the discovery. The vikings themselves probably had no idea how big North America was when they discovered it and probably thought it was just another island like Iceland. When Christopher Columbus returned to Spain he brought back stories, natives, crops, etc. He may not have been the first to discover North America, but I think you can argue that he was the first to discover the New World, and the subsequent global impact that had.