Final answer:
The Roman Empire increased the size of its professional army, offered soldiers rewards like wealth and land, and conducted reforms to prevent military overreach. Expansion was also economically motivated, securing resources and integrating conquered peoples into the Roman culture.
Step-by-step explanation:
To correct the issue of needing a large army to protect its expanding territories, the Roman Empire undertook several strategies. Initially, the army was composed of volunteer citizen-soldiers, but as the republic gave way to the empire, the military became a professional force that offered tangible rewards, including wealth and sometimes land acquired from successful campaigns, as incentives for service.
Reforms by emperors like Augustus and Diocletian were critical in restructuring the military. Augustus stationed twenty-eight legions throughout the provinces, and improved the terms of service for soldiers. Diocletian, facing threats from Persia and the Germanic tribes, reorganized the Roman army to be larger and more efficient, emphasizing the use of heavy cavalry, and strategically reducing the size of individual legions to prevent potential usurpations. Additionally, the Roman military was instrumental in assimilating conquered peoples, as service in the army required learning Latin and mingling with soldiers from across the empire, thereby promoting a unified Roman identity.
The expansion of the Roman Empire was not only for military protection but also to secure economic resources. Conquest of regions like Egypt greatly enhanced the empire's grain supply and increased the number of slaves in the Roman economy, which played a central role in industry and agriculture.