Why did the immigrants pose a challenge to the Roman Empire?

Immigrants posed a challenge to the Roman Empire primarily because of their significant numbers, which overwhelmed Roman soldiers both in terms of physical presence and military engagement. As various groups moved into Roman territory, such as the Visigoths, Vandals, and Huns, their sheer size and ability to coordinate attacks made it increasingly difficult for Roman legions to maintain control over these regions. The pressure from these populations strained the military resources of the Empire, forcing them to deploy more troops to defend against multiple incursions. As the Empire struggled to manage these threats, it led to a decline in its military effectiveness, contributing to the broader challenges that ultimately led to its downfall.