How Geography Divided Italy For 1,302 Years

From not long after the fall of the Western Roman Empire to only 150 years ago, Italy was not the unified country we see today, but a fragmented mess of kingdoms and city-states. My question is, what divided it for so long, and how does this history affect the country today?

MUSIC:
“Legio II Traiana Fortis” by David Chas
“A King’s Ransom” by Bonnie Grace*
“In the Trenches” by Jon Sumner*
“Dance of the Wildcarts” by Deskant*
“Fair Lady’s Step” by Deskant*
“Circle” by Jones Meadow*
“Across the Ocean” by Bonnie Grace*
“Grenadine” by West & Zander*
(*via EpidemicSound)