The Fall of the Western Roman Empire.
In 476AD the Western Roman Empire collapsed due to a combination of political, economic and social problems that weakened the empire so much that it could no longer protect itself from barbarian tribesmen attacking the frontiers.
From 200AD political problems continued to weaken the empire.
After the death of Commodus in 193AD the line of succession became unclear and army generals led revolts to claim the title of Emperor. During the same year Septimus Severus, Pescennius Niger, and Clodius Albinus all commanded rebellions to put themselves into command of Rome. Septimus won and was emperor until 211AD. This all led to the subsequent practice of overthrowing the emperor in order to become emperor. These were normally led be army generals who's army, instead of defending the frontiers from barbarian invaders, spent most of their time fighting among themselves.
The was also mostly made up of mercenaries from tribes outside the Roman boarders due to the Roman people believing that it may have been the end of the world and deciding to get into the barbarians. Slaves were also unwilling to fight as they saw that there was nothing to be gained for themselves. Most of the mercenaries were also corrupt making it a rather foolish thing to give them the soul responsibility to guard Rome against the encroaching tribesmen.
In 284AD Diocletian divided the empire into two separate states, the eastern and the western. Although this seemed like a good idea at the time, it proved not to be so. When the barbarians attacked western Rome the east did not help protect it.
The empire was split due to Diocletian feeling that it was too large to administrate. It also turned out that the empire was too big to defend properly. This in turn made trade become unsafe.
This caused economic problems for the Romans.
During the 450's Vandals devastated immense wheat fields that fed the Roman people, causing many of them to be unable to feed themselves and their families.
