Decline of the Roman Empire - Response to the Theory

Our group's theory was catastrophic collapse. As the theory stated, there was not one sole reason for the fall of the Roman Empire but due to multiple reasons. Reasons include external pressure, lack of unity, economic collapse, internal system's problems led to the decline. I agree with this collapse theory because a great power such as Rome does not have one sole reason that led to its demise. The reasons seemed accurate when one considers the circumstances/events which occurred during that time period such as the Barrack Emperors, Gothic and Hunnic pressure. When looked through a historical and logical standpoint, I am convinced that reasons such as external pressure, internal system's problem, economic collapse caused the collapse of the Roman Empire.