Americans don't have the experience of being divided up into smaller countries that are easily dominated by foreign powers, so we tend to underestimate the value of national unity.
But there are two sides to the question. Divided Italy and Germany easily fell under the rule of foreign powers -- France, and in Italy's case also Austria and Spain -- but arguably their greatest cultural moments came when they were still divided into smaller countries. That's certainly true of Italy.
To be fair, though, Harper's couldn't see what the 20th century had in store for Germany and Italy after unification.
Agreed, but in the case of the Italian Renaissance, those republics became relatively prosperous & powerful at a time when many other nations were divided & weak.
Indeed, if I remember right, the Italian Renaissance pretty much ended when the King of France pulled his armies together and marched to destroy those uppity Italians republics while they were unable to unite enough to resist him.
It was a pattern repeated many times, and a lesson from history on the dangers of unlimited secessions.