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During the Pax Romana the Roman Empire was stable, sophisticated, wealthy and more powerful than any of its neighbours. But then in 476 C.E, the Roman Empire declined and fell. The empire was overthrown by the  leader Odoacer, who became the first Barbarian to ever rule in Rome. There are many causes to the fall, political, economic, military and social causes. And the fact that the capital was moved to the western part just weakened the empire even more. Many people blame the initiation of Christianity, it made many citizens turn into peacemakers and people who are against war which made it difficult to defend against the barbarian tribes. However, there were more factors such as slavery, the coinage, and the inflation. The final death blow to the Roman Empire was inflicted by these Barbarians.
There were different types of emperors in Rome, those who helped the empire and those who caused corruption. Augustus who was the first emperor led Rome’s transformation from republic to empire. Constantine who was the first Christian emperor, he brought back the two halves of the empire into one, he also moved the capital to the western part of the empire, but after his death the empire divided into two again. Claudius was a deaf emperor, but he brought new efficient laws and started great building projects. During his reign, they conquered Rome. Julius Caesar never really took the title of emperor but he was still the first person to take control of the empire after the Senate. He rose to become a powerful and successful ruler, he also brought big areas of the Europe under the control of the empire. Nero was known as a cruel and greedy ruler, he used to persecute Christians in Rome, they were arrested and executed in the Colosseum. Diocletian was the emperor that split the empire into two and caused corruption. After the fall, emperors still devalued the coinage and brought on violent inflation. 
One of the causes of the fall of the empire was social causes, and to me that was one of the least important causes. The increase of slaves put many of the Romans out of work. There was disloyalty to the empire and a lack of patriotism as well as a  Contrast between the rich and the poor. The population shrinking due to starvation and disease, that made it difficult to manage  farms and government effectively. The increase of people becoming nuns and monks decreased social value. Roman world was oppressed by a new tyranny, and the persecuted sects became the secret enemies if their country. The more people became Christians the more there was loss of traditional values. But the main social cause was that most people were likely to no longer believe in the empire anymore. The Roman government had become highly corrupt and  people no longer had faith in it. And the fact that it was common for the emperors to be assassinated by other members of government or their own wives, the people were expected to believe it was for justice every single time. 
Another cause which I think is more important is military causes. Barbarians started entering Rome, the Romans did not really treat them well which caused them to become enemies. The auxiliary army grew rapidly and they became more than the legionary army. The army was basically not what it used to be, there was corruption in the military, dishonest generals and non-Roman soldiers. The legions acquired the vices of strangers and mercenaries. The emperors were more worried about their own personal safety and the public peace than actually making the empire itself better and safe. Over expansion of the empire and overspending on the military did not help. And also the weakening of the Roman legions only weakened the empire.  There were many civil wars in Rome between usurpers and emperors, which just added on the conflict in Rome. The chaos interrupted military training and  Some emperors started hiring foreign mercenaries in the military and they were not loyal to Rome at all. But also there was an inability in recruiting soldiers. Bureaucrats and soldiers were being paid in merchandise such as grain. 
Another cause was political causes which is the second most important to me. The fact that the empire was divided and when the capital was then moved only weakened it even more. The empire was too large to govern effectively. The emperors would constantly switch and they could not settle on one. Civil wars broke constantly but between different political groups.  Both the Eastern and Western part of the empire failed to work together, and the eastern part was scared that the west would attack them. The over expansion of the empire gave Rome a lot of trouble, they had to over see the whole area that they controlled which was pretty hard. Emperors were often selected violence or by birth, so the head of government was always a capable leader. The rich became lazy and showed little interest in trying to solve Roman problems. There was corruption in the government and there was a lot of political instability. Also, the Eastern Empire rose and was becoming more powerful than the Western Empire. 
For me, the most important causes were the economic causes because I feel like they were the most effective. After there was increase in taxing and incoming attacks or threats, many rich people fled the country which led to Rome losing a of of money.  There was a high rate of inflation because there was a lot of money being made so the money lost its value. The inflation led to high rates of tax, and it caused the poor to be more troubled and the gaps between the rich and the poor expanded.  The Romans were spending an unnecessary amount of money on the military.  Slave labor was good for the rich people because it was cheap, but it caused a lot of farmers to loose their jobs. The prices of taxes increased, and that caused for the trade in the empire to decrease. When goods became the same price all over the empire, it suppressed trade and profit. The prices were driven so high by theme men that in one purchase a soldier was deprived of his bonus and his salary. The value of the currency is the empire was completely lost. There was an over reliance on the slaves and that caused corruption.