Final answer:
The fall of the Roman Empire was caused by a mix of internal issues such as cruel emperors and political turmoil, and external pressures including barbarian invasions and conflicts with the Sassanid Persians, leading to a weakened state and loss of territories.
Step-by-step explanation:
The decline of the Roman Empire was a complex process influenced by both internal and external factors. Some of the issues that led to the fall of Rome include attacks from barbarian tribes, cruel and incompetent emperors, economic hardship due to loss of territories in the west which led to reduced tax revenues, and political instability within the Empire itself, with many emperors being murdered or dying in battle over a short time span. Additionally, the Roman military faced serious threats as barbarian groups became more populous and better-organized, able to defeat large Roman forces in what followed a 'barbarian domino effect' that disintegrated the western Empire.
The increase in pressure from foreign invaders on the Roman borders, such as the aggressive Sassanids seizing control of Persia and challenging Rome, further strained the Empire's resources. Internally, factors like factional politics, nationalism, and the retreat of Roman elites to their vast estates contributing to societal divisions and weakening of the state's foundations also played critical roles in the Empire’s demise. Ultimately, while the city of Rome and the western half of the Empire fell, the eastern half, with its capital in Constantinople, continued to survive under constant military pressure until 1453.