The Dark Ages.
According to westernreservepublicmedia.org:
“The Middle Ages, or medieval time, is generally believed to have started with the fall of the Roman Empire in 476 and to have lasted about 1,000 years until about 1450. The beginning of the Middle Ages is called the Dark Ages because the great civilizations of Rome and Greece had been conquered by barbarians.”
As a result of constant invasion by barbarians tribes, the civilization which had flourished under the rule of the Roman Empire came to standstill.
Similarly, development in learning, architecture, science, and art slowed down or stopped altogether.
So because of the many wars between the petty kingdoms, life became unsafe.
A kind of darkness covered life in Europe. For this reason, the period from about A.D 450 to 800 is sometimes called the “Dark Ages” (it is interesting to note that this is the period when the old kingdom of Ghana reached the peak of its civilization.)
Europe remained in this over 500 years before there was any real rebirth of interest in learning and culture.
Meanwhile, it would be wrong, however, to think that there was no progress of any kind in Europe during the Dark Ages.
So, a certain amount of learning and art was kept alive by the church. (The work of the monks was chiefly responsible for keeping alive some aspects of learning and art.)
A factor that helped to bring the Dark Ages to an end was the emergency of a United empire in about the ninth century.
This united empire was chiefly the work of the emperor Charlemagne, or Charles the Great, as he is often called.
According to Wikipedia, emperor Charlemagne or Charles the Great, numbered Charles I, was the King of the Franks from 768, the King of the Lombards from 774, and the Emperor of the Romans from 800.
It was during the Early Middle Ages, that he united the majority of western and central Europe. His action later helped to bring the Dark Ages to an end.