I have found many different answers on the internet and in books. But is there one big frank answer? :confused:

Thanks.

In one big frank answer : It was too big and had a huge area to support. Governing over wide areas usually causes many internal conflicts.

Rome actually fell to a tribe called the Visigoths, where the word goth comes from. Romulus Augustus was the last Roman emperor. Constantine, the first Christian emperor and in 313 announced the 'toleration' of Christianity in The Edict of Milan, he is also Romulus for the Nicene Creed which is still used in most protestant churches today. In about May of 330 Constantinople was christened the new capital of Rome. This of course weakened the powerful empire of Rome which was already declining and this act just divided the empire even more. The Visigoths actually allied with Rome in 394 and the Roman empire was split. The Visigoths were a germanic tribe who were allowed the freedom to move further south into the Roman empire by the emperor Valens, who later recanted and refused to let them settle. The began to battle starvation and revolted. The Visigoths sacked the Balkan peninsula and took control over Rome in 410 A.D.

All true along with self indulgence, greed, loss of purpose (from the original mandates of Rome), politics and more.