Final answer:
The invaders' movements during the fall of the Roman Empire included both quick conquests and gradual migrations, making both explanations plausible. The Goths and Vandals conquered swiftly, while groups like the Angles and Saxons migrated and settled, establishing new kingdoms.
Step-by-step explanation:
The question of whether the invaders were moving quickly to conquer Rome or if it was more of a migration of people is a complex one. The information provided indicates that some groups like the Goths and Vandals did indeed move quickly to conquer territories once part of the Roman Empire. The Goths sacked Rome in 410 and afterwards were given land in southern Gaul, while the Vandals passed through Spain and went on to conquer Roman North Africa. However, there is also evidence of more gradual migrations, such as the Angles and Saxons moving into Britain and forming various kingdoms which later united to become England. Considering the various movements of different tribes and the pressures from external forces like the Huns, it seems reasonable to say that both conquest and migration were occurring.
Based on the provided evidence, the most accurate answer would be D) Both A and B are plausible explanations. This takes into account the rapid conquests of territories, as well as the establishment of new kingdoms, which is characteristic of migration and settlement over time.