The Duchy of Saxe-Gotha-Altenburg was a historical state in Germany, formed in 1826 through the merger of the Duchies of Saxe-Gotha and Saxe-Altenburg. It was part of the larger region known as the Saxon duchies, which were ruled by members of the House of Wettin. The duchy was located in the central part of Germany and played a role in the political landscape of the time. The capital of the duchy was Gotha, which was known for its cultural contributions, including the famous Gotha Book Fair. The duchy existed until 1918, when the German monarchy was abolished after World War I, leading to the establishment of the Free State of Saxe-Gotha-Altenburg.