Final answer:
The Roman army became formidable due to strategic innovations such as 'divide and conquer' and the professionalization of soldiers, which led to a disciplined, loyal, and constantly ready fighting force.
Step-by-step explanation:
Two significant innovations that contributed to the prowess of the Roman army include the development of sophisticated military tactics and the professionalization of soldiers. The tactic of divide and conquer was instrumental in allowing Rome to single out and focus its military efforts on defeating one adversary at a time, rather than facing coalitions of enemies. This approach, combined with their strategy of turning enemies against one another, and the policy to negotiate from strength, ensured that the Romans rarely found themselves at a disadvantage on the battlefield.
Furthermore, the transition from a volunteer army to a standing professional force meant that soldiers were not only more skilled due to their constant readiness for battle, but they were also loyal, as they were now career soldiers with tangible rewards promised to them by generals. The Roman legion, a military unit consisting of approximately five thousand soldiers, became a cornerstone of this professional army. With strict discipline and incentives like wealth distribution after victories, Roman soldiers were highly motivated and maintained exceptional unit cohesion. Additionally, they were equipped with practical innovations like well-constructed roads for rapid mobilization, which further cemented Rome's military dominance.