Prologue:
In the course of history, there have been three major discoveries of America. The first discovery was made by Asians from 30,000 to 10,000 years ago. These Asians followed herds and plants across a landbridge across the Bering Strait. They came in waves for 20,000 years because the landbridge was sometimes flooded, stopping migration. The second discovery of America was by the Vikings, who discovered America in 986 CE. However, the Vikings got in fights with the Native Americans, and abandoned their settlement permanently around 1010. The third and probably most famous discovery was by Christopher Columbus, who, in 1492, sailed the ocean blue. I will not go into further detail about Colombus' discovery, since it is already described in detail in Biblos' writeup in this node. Rather, I will attempt to answer this question: which discovery was the most important?
ON THE IMPORTANCE OF THE DISCOVERIES OF AMERICA
Most people would say that the Viking discovery of America was the least important, since it did not have much historical significance. This is due to the fact that the Vikings remained on the continent for only a small amount of time. In this short period of time, they did not interact much with the natives or with the environment. They left barely any permanent marks, and didn't really learn anything new before they fled. The Viking discovery of America could be removed from history and nobody would ever notice.
Or would they? Christopher Columbus found many of his father-in-law's papers, which include interviews with sailors and maps of the ocean. Since the knowledge of the Vikings was spread widely through the North Atlantic, which Columbus knew like the back of his hand, it is very possible that he learned about the Vikings' quest to America. It is also possible that these tales are part of what made of him sail west. Therefore, it is very possible that, if the Vikings had never made it to America, Columbus never would have either. This would have extreme phistorical significance]. That would leave the first discovery as the least important.
Or would it? If the first discovery never happened, then the Vikings would probably colonize America themselves. It is very likely that we would never have heard of Columbus, and that the United States, or its equivalent, would be a Viking-ruled country. This would mean that the first discovery is very historically significant, for had it not happened, the Vikings would rule the Americas. So, now that we have said that the first and second discoveries are both very historically significant, we must conclude that the third discovery is the least important.
Or can we? If the third discovery were never to happen, then it is very likely that we would not be here today. The Native Americans would grow and advance. They might have fought amongst or banded with each other until there were a few large countries in the Americas. Or, they might develop like Africa, with many, many countries on the continents. They would probably come find the Europeans. In either, case, the world would be very, very different. So, due to the circular nature of this argument, unless one can disprove one of the arguments presented here, one must conclude that all the discoveries are equally important. In any case, this writeup would be a lot easier to write if America had never been discovered.
Epilogue:
Or would it? If America didn't exist, it is probably safe to say that the technological revolution...
Sources:
Mostly: rdude's brain
Sort of: Garrraty, John A. The Story of America, Volume 1. Chicago, US: © 1992 Holt, Rinehart and Winston, Inc.