What did mercenaries have to do with the decline of the Roman Empire?

Explanation: Supreme military discipline and training served as the foundation for the construction of the Roman Empire. However, when the Empire grew in size and began to fragment, the Western Empire could not maintain its superior military strength anymore. As a result, it began to rely on mercenary forces, typically composed of barbarians. The armies were not disciplined and had no loyalty to the Empire. Therefore, the military structure was unable to maintain its integrity. And as soon as that occurred, the political system came crashing down. At various points in antiquity, the mercenary soldiers would turn against the Romans and begin to demand or grab land for themselves. For example, Alaric, the Gothic ruler who eventually conquered Rome, was formerly a Roman mercenary leader before becoming king.

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