I was looking at this page on Wikipedia and noticed the massive differences in per capita GDP between North and South Italy. Northern Italy looks more like Germany or Japan, Southern Italy looks like Mexico or Brazil. I was curious how these differences compared to those in other major European countries, so I checked Germany and France -- if you exclude East Germany, neither one has wealth differences so striking (and even if you include East Germany, Germany's wealth differences are still no worse than Italy's)
Why is this? I understand how perhaps there were smaller populations and fewer natural resources in South Italy, but I'd be surprised if that was the full story. Are there clear historical reasons that Southern Italy did not develop as much as the North?
The south was under the thumb of a fairly strong monarch for about 700 years, from about 1100 to 1800. The north escaped that fate.
The data throughout Europe tend to show that "absolutist monarchs stunted the growth of commerce and industry" (DeLong). Southern Italy seems to have been an especially pronounced case.
From about 1100 to 1800, Italy's south was under the rule of foreign-derived kings -- first the Norman kingdom of Sicily, then the Angevin and later Habsburg kingdoms of Naples. That's 700 years where the best money and opportunity in the south are at royal courts.
Meanwhile, in the north, there aren't equivalent kings, and the best money and opportunity remains in the cities -- in doing business.
Mind you, I don't think economic historians have a settled agreement why strong kings were bad for commerce and industry. It might be "money that could be invested went to taxes instead, spent on war or royal generosity instead of business". Or it might be "people focus on competing for royal favor instead of competing to make great products."
And obviously a strong king has some military advantages -- look at Machiavelli's and others' complaints about (divided, northern) Italy's weakness against French and Spanish invaders.
But in general, too strong a king seems to have been bad for a country's long-term economic growth. Southern Italy had 700 years of such kingship that northern Italy escaped.
Source: Princes and Merchants: European City Growth before the Industrial Revolution, by J. Bradford De Long, Andrei Shleifer