Final answer:
Migration out of Rome occurred due to land dispossession after military service, population growth, economic transformations, social shifts such as urbanization and the decline of feudalism, and the expulsion of certain ethnic groups.
Step-by-step explanation:
The migration of 950,000 people out of Rome can be attributed to several factors. During the time of the Roman Republic, numerous Roman citizens, who owned small family farms, found themselves serving as soldiers in the Punic Wars, which led to prolonged absences from their homes. Upon return, many discovered their properties in the hands of others, prompting some to abandon their farms and move to Rome, swelling the ranks of the urban proletariat.
Rome's population growth also featured the expansion of the city due to migrants seeking new opportunities, reflective of its founding narrative as a place of asylum. Meanwhile, highly efficient technology fostered commerce among the provinces, leading to economic transformations that encouraged migration. Furthermore, during the Migration Period, there was a large-scale reorganization of territories, which also instigated movements of people.
In later centuries, societal shifts such as the decline of feudalism, the rise of cities, and the resultant agrarian revolution and development of commerce saw substantial migration from countryside to city, with Italy becoming the most urbanized society of that time. Occasionally, Rome expelled various ethnic groups, reflecting the complex dynamics of immigration and legal status of the city's inhabitants.