Complex sentence: The rising trend in population growth continued until the mid- 1980s, when the "comune" had more than 2.8 million residents; after that, population started to decline slowly as inhabitants began to move to nearby suburbs of Rome.
Split into simpler sentences: The rising trend in population growth continued until the mid- 1980s, when the "comune" had more than 2.8 million residents. After that, population started to decline slowly as inhabitants began to move to nearby suburbs of Rome.