I'm reading "Journey to a Revolution" by Michael Korda, and he has a throwaway line about how army officers who emigrated after Kossuth's failed revolution ended up in high command in the Union Army during the civil war. Is this true? If so, what kind of impact did the Hungarians have in the war?
Yes, it's absolutely true. Check out this answer I gave a month ago to someone's question about foreign volunteers during the American Civil War. One of the more famous examples of Hungarian involvement in the war is on the staff of Gen. Franz Sigel. That Union general employed quite a few Hungarian officers -- and enlisted men, too.