Grand Duchy of Hesse–United States relations
The Grand Duchy of Hesse and the United States began relations in 1829 with mutual recognition going through expansion in 1868 when the grand duchy joined the German Empire in 1871. Relations would eventually end with World War I when the U.S. declared war on Germany.
Source: Wikipedia — Grand Duchy of Hesse–United States relations (CC BY-SA 4.0)