The Grand Duchy was abolished in 1918 with the other German monarchies , and the state joined others to form the new state of Thuringia in the Weimar Republic . The Grand Duchy came to an end in the German Revolution of 1918 â `` 19 with the other monarchies of the German Empire . It was succeeded by the Free State of Saxe-Weimar-Eisenach , which was merged into the new state of Thuringia two years later .