During the Austro-Prussian War, the Duchy of Nassau fought on the side of Austria.

On the losing side, the Duchy of Nassau was annexed to Prussia on October 3, 1866, ceased to be an independent sovereign state ending relations.

This convention was concluded in Berlin between U.S. Minister to Prussia Henry Wheaton and Nassau’s Minister to Prussia Col. and Chamberlain Otto Wilhelm Carl von Roeder.

[1] The first U.S. Consul appointed to the Duchy of Nassau was John B. Muller Melchiors on November 1, 1853.

[2][3] This article incorporates public domain material from "A Guide to the United States' History of Recognition, Diplomatic, and Consular Relations, by Country, since 1776: Nassau".