Short answers, pulled from the story.
Italy's Middle Ages are generally defined as the period between the collapse of the Western Roman Empire and the Italian Renaissance. The conventional starting point is 476, when the last Western Roman Emperor was deposed. The period closed as the Italian Wars, beginning in 1494, drew foreign powers into the peninsula.
Theodoric the Great was the Ostrogothic king who defeated Odoacer on the 25th of February 493 and ruled Italy through Roman administrative personnel. He had lived in Constantinople and governed a largely Roman population under Roman laws. His reign is considered a period of recovery: infrastructure was repaired, the economy was tended, and the philosopher Boethius served as his minister.
The Exarchate of Ravenna was the administrative territory that Byzantine forces controlled in central-northern Italy after the Lombard invasion, covering areas corresponding to modern Lazio, Romagna, and a corridor through Umbria. It was abolished in 751 when the Lombards seized Ravenna, ending the Byzantine presence in central Italy.
Northern and central Italian communes began transforming into self-governing city-states in the 11th century, modelled consciously on ancient Roman republicanism. The Holy Roman Emperor was an absentee ruler, and the collapse of the Margraviate of Tuscany after the death of Matilda of Canossa in 1115 left a power vacuum that wealthy cities filled. Cities such as Venice, Milan, Genoa, Florence, Siena, and Pisa rose as major financial and trading centers.
The Peace of Lodi was an agreement that established the Italic League in 1454, initiated by Francesco I Sforza of Milan. The five member states were the Venetian Republic, the Republic of Florence, the Duchy of Milan, the Papal States, and the Kingdom of Naples. The league brought the first period of relative calm to the peninsula in centuries.
The Black Plague struck in the 1340s and 1350s and wiped out close to half of Europe's people, with the heaviest losses among young working-age adults. In cities such as Florence, Verona, and Arezzo, more than 15 percent of residents were over the age of 60 after the plague. The countryside depopulated as survivors moved to cities, and in early 15th-century Florence the average age of the lower classes was 25 while the upper classes averaged just 17.