Answer :
"C. The Roman army was strong, but was still unable to defend Rome from the Visigoths" correctly describes events that led to the fall of Rome, although there were internal issues as well.
The correct answers are A and B, here is a brief explanation of each one of them :
A. The fate of Rome was partially sealed at the end of the third century, when Emperor Diocletian divided the Empire into two halves - the Empire of the West, based in the city of Milan, and the Empire of the East in Byzantium, later known as Constantinople. The division made the empire more easily governable in the short term, but over time the two halves were moving away. The West and the East failed to work together adequately to combat external threats, as well as constantly disagreeing on military resources and aid. As the distance increased, the Empire of the East, where the majority of the population spoke Greek, enriched, the West, which spoke Latin, fell into an economic crisis. More importantly, the strength of the Eastern Empire served to divert the barbarian invasions of the West. Emperors such as Constantine ensured that the city of Constantinople was fortified and well protected, but Italy and the city of Rome - which had only symbolic value to many in the East - were vulnerable. The Western political structure would finally disintegrate in the fifth century, but the Eastern Empire somehow managed to resist for another thousand years before being conquered by the Ottoman Empire in the 1400s.
B. The barbaric attacks on Rome were partially the result of a mass migration caused by the invasion of the Huns into Europe in the late fourth century. When these Eurasian warriors invaded through northern Europe, they pushed many Germanic tribes to the borders of the Roman Empire. On the contrary, the Romans allowed members of the Visigothic tribe to cross south of the Danube to find security in the empire's territory, but treated the migrants with extreme cruelty. According to historian Ammianus Marcellin, Roman officials even forced the hungry Goths to offer their children as slaves in exchange for dog meat. By brutalizing the Goths, the Romans created a dangerous enemy within their own borders. When oppression became unsustainable, the Goths revolted, eventually killing the valiant emperor of the Eastern Empire during the Battle of Adrianople in AD 378. Shocked, the Romans negotiated a fragile truce with the barbarians, which ended in 410 when the Goth king Alaric went to the West and sacked Rome. With the Empire of the West weakened, Germanic tribes such as the Vandals and Saxons were able to cross the borders and occupy Britain, Spain and North Africa.
