Short answers, pulled from the story.
Rome began as an Italic city-state before evolving from a kingdom into a republic between 753 BC and 509 BC. Historical evidence confirms this transition period for the ancient Roman state.
The Italian peninsula was dominated by diverse tribes including Gauls, Ligures, Veneti, Camunni, and Histri in the north. These distinct communities existed long before Roman expansion created a single political entity.
Around 7 BC Augustus divided Italy into eleven regiones as reported by Pliny the Elder in his Naturalis Historia. This organization brought over two centuries of stability and allowed agriculture, handicraft, and industry to flourish.
Emperor Diocletian moved the imperial residence associated with western territories from Rome to Mediolanum in 286 AD. He also subdivided Italy into provinces and ended its special juridical privileges which led to loss of precedence over other regions.
Alaric king of Visigoths sacked Rome itself in 410 something that had not happened for eight centuries. Northern Italy faced attacks from Attila's Huns in 452 before Rome was sacked again in 455 by Vandals under Genseric.