Possible Major Causes:
Conflict between the Emperor and the Senate
Weakening of the emperor’s authority (after Christianity the Emperor was no longer seen as a god)
Political Corruption – there was never a clear-cut system for choosing a new emperor, leading the ones in power to “sell” the position to the highest bidder.
Money wasting – the Romans were very fond of their prostitutes and orgies and wasted a lot of money on lavish parties, as well as their yearly “games”