Grand Duchy of Mecklenburg-Strelitz–United States relations
The Grand Duchy of Mecklenburg-Strelitz and the United States mutually recognized each other in 1853, but never formally established diplomatic relations. Relations continued when the grand duchy joined the German Empire in 1871.
Source: Wikipedia — Grand Duchy of Mecklenburg-Strelitz–United States relations (CC BY-SA 4.0)