The United Baltic Duchy was a attempted Prussian (German) puppet state that was set up across Estonia and Latvia in September 1917 and fell in June 1919. The proposed state erratically came in and out of existence until it's final collapse 2 years later. The states would have been in a personal union with the Crown of Prussia and subordinate to it. It was a planned buffer state that was proposed by both the Baltic German and exiled Russian nobility after the Russian revolution and German occupation of the Russian governorates of Courland, Livonia and Estonia.
Lithuania and Belarus were also to be added if the plans had worked out after falling under the German Empire's occupied territory Ober Ost.
The Baltische Landeswehr (Baltic Land Defence) was the name of the unified armed forces of the Germanic Couronian and Livonian nobility that lasted from 7 December 1918 to 3 July 1919. They planned to make it a German puppet state, but only Germany was interested in the idea and the local did not want German or Russian rulers in their lands.
Bolshevik Russia tried to set up the Latvian SSR of 1919-1920 in the east of Latvia.