Chapters 3, 4, and 5 of my 2013 Cambridge University Press book, U.S.-Habsburg Relations from 1815 to the Paris Peace Conference: Sovereignty Transformed deal with US consuls in the Habsburg Empire and Habsburg consuls in the United States, particularly as they attempted to deal with the effects of migration between the two countries in a period when passports were not required; questions about citizenship were rife.
Chapter 3 offers a broad history of the US Consular Service, stressing the expansion of its mandate from facilitating trade to promoting trade and then protecting citizens abroad. As I have done more research on consular services, I do think that trajectory holds for the US presence in the Habsburg Empire, but consuls in other parts of the world performed the full range of functions from the beginning of the service’s existence. Each individual post had its own unique profile of activities.