Prohibition in the United States had a global effect, scattering bartenders from America around the world. Sure, there were still a lot of drinks poured in the US, but many of the best mixologists moved to places where they could legally practice their craft. And they took their training, knowledge, recipes, and libraries with them.
Long after Gaspari Campari took his inspiration from Antonio Carpano to create both his bitters and a great drink, the Torino-Milano which later became known as the Americano, what were they drinking in the center of Italian fashion?
I recently found this interesting recipe booklet: