Explanation: Oftentimes, Rome would ‘subsidize’ vassal states on the frontier. In early periods it was actually very effective. Roman ‘subsidies’ to their client states reinforced the power of pro-Roman elites and improved the capabilities of the clients to repel their neighbors - which was usually their primary purpose, as buffer states.

… but by the Late Empire, when the barbarian tribes were more desperate to get into the Roman Empire to escape enemy tribes and climate change, not just seeking loot and glory; and when the Empire’s own military forces had degraded, especially in comparison to the barbarian tribes, it was… probably quite counterproductive.