Paris's suburbs account for its metropolitan growth in the 20th century, with the new comers a mix of people from beyond European France and probably rural and small town folk as well.
During the mid-20th century, Madrid and, a little later, Barcelona grew due to in-migration from rural areas, attracted by industrial jobs. Milano had similar growth and causes, with the in-migration coming from the nation's south. Roma's growth began earlier, with earlier redevelopment financed by the national dictator.