According to mazzini, why should italy be united

Mazzini believed Italy should be united as one country because all Italians shared a common nationality and cultural heritage.

Details:

Giuseppe Mazzini (1805-1872) was a powerful promoter of Italian nationalism during the 19th century, at a time when the Italian peninsula was divided into many smaller entities.  He founded the group known as Young Italy and was a major figure in the Italian unification movement known as "Risorgimento" ("rising again").  He was a strong voice calling for all Italians to unite together in a republic.  Let me quote you a bit from Mazzini, an example of his persuasive style:

Italy did not finish its nationalist program of unification as soon as Mazzini would have wanted.  A united Italy finally came together in 1871, not long before Mazzini's death.  But he had been a pioneer of the movement that brought Italians together during his lifetime.

by creating a labor shortage that pushed the continent toward a market economy