What made Christianity appealing during the fall of the Roman Empire?

Answer 1

Some historians believe that Constantine's interest in Christianity was because he saw it as a potential force for unity in the Roman Empire, with its strong discipline and well-defined hierarchy. He was dismayed to find that Christianity was not at all united even within itself, and eventually found that Christianity did not help him create a united empire.

In any case, the Roman Empire only remained united until 394 CE, just 14 years after Christianity became the official religion of empire. The split was not directly caused by Christianity, just the size and unwieldly nature of the empire. The fall of Rome is conventionally dated to 476 CE, less than 100 years after Christianity became the official religion of empire. The former empire of Rome began to fragment into kingdoms, and Christianity began to disappear in the provinces.

The Eastern Empire survived much longer, but was destroyed in the aftermath of the sack of Constantinople by Western Crusaders during the Fourth Crusade. This fragmentation can be very much blamed on the Crusades, and therefore on a Christian enterprise authorised by the Pope, although the sacking of Constantinople was outside his control.

Answer 2

While earlier cults which promised an after life required people to make long and exppensive visits to the cult centre, others sprang up which came to the customer - Mithras, Judaism, Christianity, Isis etc etc. And when Christianity was given official supremacy, it eliminated competitors, killing the priests of Mithras on their altars and burying the temples, and absorbing Isis into the person of Mary. Given official authority and elimination of competitors, it had an unchallenged appeal.