The Middle Ages, a period in European history that followed after the fall of the Western Roman Empire is usually dated to year 476 when Germanic chieftain Odoacer deposited the last Western Roman Emperor, Romulus Augustulus. The event is traditionally considered as the end of the classical antiquity and beginning of the Middle Ages.
On the other hand, year 476 is not universally accepted as the beginning of the Middle Ages because the empire was already in ruins when Odoacer deposited Romulus Augustulus. The decline of the western half of the empire dates back to the 3rd century when it almost collapsed due to economic crisis, civil war and external threats.
The Roman Empire managed to survive the so-called Crisis of the 3rd Century but the latter caused far-reaching economic, social, cultural and institutional changes that greatly contributed to the fall of the Western Roman Empire. After the empire permanently split into two halves in 395 the western part became unable to repulse the barbarian invasions. The Western Roman Emperors were forced to allow the barbarian tribes to settle on the Roman territory in return for providing military assistance.
The barbarian military leaders turned against the Roman authorities from time to time and larger stronger over time. The Western Roman Emperors were rulers only formally after the mid-5th century, while the real power was de facto in the hands of barbarian military leaders. Odoacer therefore overtook the rule from Romulus Augustulus only formally. The deposition of the last Western Roman Emperor was culmination of a process that started a lot earlier and has not caused any major disruption at the time.
Due to the fact that the process that led to fall of the Western Roman Empire took place gradually some historians do not consider the deposition of Romulus Augustulus by Odoacer as the end of the classical antiquity and beginning of the Middle Ages. They claimed other events with far-reaching impact on the course of history such as the beginning of the Migration Period (375), the Battle of Adrianople (378), permanent division of the Roman Empire into two halves (395), the Sack of Rome (410) and death of the last de jure Western Roman Emperor Julius Nepos (480). In addition, some scholars suggested events related to religion which has played a major role through medieval times. Some of the most common religion-related start dates for Middle Ages include the issue of Edict of Milan (313) that ended the persecution of the Christians, closure of the last pagan school in Athens (529) and the Muslim contract of North Africa 647).