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Explanation:1. Invasions by Barbarian tribes
...The most straightforward theory for Western Rome’s collapse pins the fall on a string of military losses sustained against outside forces. Rome had tangled with Germanic tribes for centuries, but by the 300's “barbarian” groups like the Goths had encroached beyond the Empire’s borders. The Romans weathered a Germanic uprising in the late fourth century, but in 410 the Visigoth King Alaric successfully sacked the city of Rome. The Empire spent the next several decades under constant threat before “the Eternal City” was raided again in 455, this time by the Vandals. Finally, in 476, the Germanic leader O.d.o.a.c.e.r staged a revolt and deposed the Emperor Romulus A.u.g.u.s.t.u.l.u.s. From then on, no Roman emperor would ever again rule from a post in Italy, leading many to cite 476 as the year the Western Empire suffered its deathblow.
2. Economic troubles and over reliance on slave labor
...Even as Rome was under attack from outside forces, it was also crumbling from within thanks to a severe financial crisis. Constant wars and overspending had significantly lightened imperial coffers, and oppressive taxation and inflation had widened the gap between rich and poor. In the hope of avoiding the taxman, many members of the wealthy classes had even fled to the countryside and set up independent fiefdoms. At the same time, the empire was rocked by a labor deficit. Rome’s economy depended on slaves to till its fields and work as craftsmen, and its military might had traditionally provided a fresh influx of conquered peoples to put to work. But when expansion ground to a halt in the second century, Rome’s supply of slaves and other war treasures began to dry up. A further blow came in the fifth century, when the Vandals claimed North Africa and began disrupting the empire’s trade by prowling the Mediterranean as pirates. With its economy faltering and its commercial and agricultural production in decline, the Empire began to lose its grip on Europe.
3. The rise of the Eastern Empire
...The fate of Western Rome was partially sealed in the late third century, when the Emperor Diocletian divided the Empire into two halves—the Western Empire seated in the city of Milan, and the Eastern Empire in Byzantium, later known as Constantinople. The division made the empire more easily governable in the short term, but over time the two halves drifted apart. East and West failed to adequately work together to combat outside threats, and the two often squabbled over resources and military aid. As the gulf widened, the largely Greek-speaking Eastern Empire grew in wealth while the Latin-speaking West descended into economic crisis. Most importantly, the strength of the Eastern Empire served to divert Barbarian invasions to the West. Emperors like Constantine ensured that the city of Constantinople was fortified and well guarded, but Italy and the city of Rome—which only had symbolic value for many in the East—were left vulnerable. The Western political structure would finally disintegrate in the fifth century, but the Eastern Empire endured in some form for another thousand years before being overwhelmed by the Ottoman Empire in the 1400's.
4. Over expansion and military overspending
...At its height, the Roman Empire stretched from the Atlantic Ocean all the way to the Euphrates River in the Middle East, but its grandeur may have also been its downfall. With such a vast territory to govern, the empire faced an administrative and logistical nightmare. Even with their excellent road systems, the Romans were unable to communicate quickly or effectively enough to manage their holdings. Rome struggled to marshal enough troops and resources to defend its frontiers from local rebellions and outside attacks, and by the second century the Emperor Hadrian was forced to build his famous wall in Britain just to keep the enemy at bay. As more and more funds were funneled into the military upkeep of the empire, technological advancement slowed and Rome’s civil infrastructure fell into disrepair.
