The end of the Roman Empire marks the beginning of the Darkest Ages in Europe's history: war, tyranny poverty, famine, cold and disease, that would last for centuries.
The exact starting and, specially, ending dates of the Middle Ages are issues of controverse, as shows the discussion in Yahoo! answers. Within the scope of this timeline however, we take 476, the definite fall of Rome as the start and 1492 as the end, when Colombo definitely proves the earth is not flat, a very strong and typical middle age believe.
Further references on the fall of Rome:
The transition from the backward and supersticious Middle Ages -dominated by a world view purely based on beliefs and fears- into the Renaisance and the Modern Era -where knowledge becomes more and more based on objective, observable facts that can be proved, as science and mathematics had always been in Ancient Civilizations like the Egyptians, the Greek and the Romans- happened over a period, in which where several events took place in a relatively short span of time:
Copernicus and the Scientific Revolution - Past is Present
Just the facts: The Scientific Revolution, part 1
Turning points in History
Native America before European Discovery & Colonization
While European "civilization" in the Middle Ages had been immersed in constant battles for power, tyranic religious oppression, poverty, famine, disease and in general, misery, paralelly there was a whole continent, ten times greater than Europe, where multiple civilizations, totaling possibly 100 million people, had thrived for thousands of years, living in relative peace and in relative harmony with their natural surrounding.
Unfortunately quite soon after the "discovery" of America, America as it originally was, both in human civilization as in natural environment, was invaded, destroyed or killed by greedy European colonialists, in search of wealth and power and anxious to impose their will and "civilization" upon whatever they encountered, without any considerations.