Roman Empire

The Romans just lacked the resources to maintain such a vast empire that greatly contributed to its eventual fall.
             Besides Rome's economic difficulties, her military might suffered greatly during the last few centuries of the empire's existence for a variety of reasons. Rome's lack of security allowed the barbarians to topple what had been the most powerful empire in the world. The massive Roman army, with about 200,000 soldiers, eventually disintegrated into an unorganized force. The largest factor, which led to the Roman army's disarray, was the attrition sustained at the hands of the barbarians during many armed conflicts. In addition to this was the increased reliance upon mercenaries, divisiveness among the units, and lack of incentives for citizens to enlist caused the Roman army to lose much of its fighting prowess.
             One of the main factors that led to the army's decline was the lack of soldiers with a Roman background. This was due to the fact that Rome gave citizenship to all free men, which took away the incentive of Roman citizenship from those willing to fight. If one did not have to risk his life for citizenship that was being offered for nothing, why fight? That was what many free men thought and that led to the Roman reliance upon mercenaries. Also, Rome's population was declining and the number of capable men declined as well. Due to free citizenship and the lack of available manpower Rome's army was rendered virtually irrelevant. This, in turn, allowed the opportunistic Barbarians to invade a weakened Rome and gradually take over the empire. (Fall of Rome).
             Although Rome's crippled economy and the disintegration of the military were huge factors in Rome's decline and fall, the progression of time itself was also a probable cause of the fall. During the span of Rome's decline and fall, many social changes were occurring and the Romans simply could not cope quickly enough to sustain their empire.