In the summer of 1861, an American diplomat in Turin, then the capital of Italy, looked out the window of the U.S. legation to see hundreds of young men forming a sprawling line outside the building. Some wore red shirts, emblematic of the Garibaldini who had fought the previous year with Giuseppe Garibaldi and, during their campaign in southern Italy to unite the country, were known for pointing one finger in the air and shouting l’Italia Unità! (Italy United!). Now …