The United Baltic Duchy (in German: Vereinigtes Baltisches Herzogtum) was a shortlived construct in 1918 made possible through Germany's occupation of Latvia and Estonia before the end of World War I.

On March 8 and April 12 1918 the local Baltic German-dominated Land Council of Courland and the United Land Council of Livland, Estland, Riga and Ösel had declared independent states, known as the Duchy of Courland and the Baltic State (Baltischer Staat), respectively. Both states proclaimed themselves to be in personal union with Prussia, although the German government never responded to acknowledge that claim.

The Baltic lands were nominally recognized as a sovereign state by Kaiser Wilhelm II only on September 22, 1918, half a year after the newly Soviet Russia had formally relinquished all authority over its former Imperial Baltic provinces to Germany in the Treaty of Brest-Litovsk. On November 5, 1918, a temporary Regency Council (Regentschaftsrat) for the new state lead by Baron Adolf Pilar von Pilchau was formed on a joint basis from the two local Land Councils.

The capital of the new state was to be Riga. It was to be a confederation of 7 cantons: Courland, Riga, Lettgallen, South Livland, North Livland, Ösel, and Estland, the four first cantons thus covering the territory corresponding to today's Latvia and the latter three corresponding to today's Estonia.

The first head of state of the United Baltic Duchy was to be Adolf Friedrich, the Duke of Mecklenburg-Schwerin, not as a sovereign monarch, but as a subordinate to the German Kaiser, similar to other dukes and grand dukes of the German Empire. Duke Adolf Friedrich never assumed office. The appointed Regency Council consisting of four Baltic Germans, three Estonians and three Latvians functioned until November 28, 1918, without any international recognition, except from Germany.

The defeat of Germany in World War I in November 1918, followed by the defeat in 1919 of the Baltic-German Landeswehr and German Freikorps units of General Rüdiger von der Goltz in Latvia by the Estonian army and nationalist Latvian units rendered the pro-German Baltic Duchy proto-state irrelevant. The Baltic nations of Estonia and Latvia were established as republics.

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Estonian Liberation War

The Estonian Liberation War (Estonian: Vabadussõda, literally "freedom war"), also called the Estonian War of Independence, in 1918-1920, was Estonia's struggle for independent state in the aftermath of World War I and the Russian Revolution.

In November 1917, upon disintegration of the Russian Empire a Diet (Maapäev), which had been elected in the spring of that year, proclaimed itself the highest authority in Estonia. Soon thereafter, the Bolsheviks dissolved Maapäev and forced the Estonian nationalists temporarily underground. A few months later, using a moment between the Russian Red Army's retreat and the arrival of the advancing German troops, the Committee of Elders of the underground Maapäev issued a proclamation the independent Republic of Estonia on February 24, 1918 and formed a provisional government. This first period of independence was extremely short-lived, as German troops entered Tallinn on the following day. The German authorities recognized neither the provisional government, nor its claim for Estonia's independence.
After Germany's defeat in World War I (November 1918) however, an Estonian provisional government was able to retake office. A new military invasion by Soviet Russia followed a few days later, marking the beginning of the Estonian War of Independence. The first Russian attacks at Narva on 22rd November were met by German and Estonian defenders but the Germans thereafter withdrew westwards. On 28th November Red Army made an assault to capture the city with an artillery support and on 29th November the Red Army captured Narva and Narva-Jõesuu. Estonian bolsheviks declared regional local government in Narva under the name of the Estonian Workers’ Commune (Eesti Töörahva Kommun) The small, poorly-armed Estonian defense force was initially pushed back by the Red Army close to the capital, Tallinn. Only 34 kilometers was a distance between Tallinn and front line. Partly due to the timely arrival of a shipment arms brought by a British naval squadron under Admiral Sinclair the Bolsheviks were stopped. In January 1919 the Estonians launched a counteroffensive under Commander-in-Chief Johan Laidoner. In this the Estonian Army was supported by the Royal Navy as well as some Finnish, Swedish and Danish volunteers. By the end of February 1919 the Red Army was expelled from the entire territory of Estonia.
Estonian troops also advanced into northern Latvia. Latvia had been declared an independent state like Estonia, but its pro-British government of Kārlis Ulmanis was toppled by a German general Rüdiger von der Goltz, who had installed a pro-German puppet government in Riga in May 1919. This was possible because under the terms of their armistice with the Western Allies, the Germans had been obliged to maintain their armies in the East to counter the Bolshevik threat. A Baltic German military unit Landeswehr, together with the "Iron Division" of the regular German army, started to advance northwards and demanded that the Estonian army end the "occupation" of parts Northern Latvia. It was widely believed that the real intent of Landeswehr was to annex Estonia into some German-dominated state like United Baltic Duchy which had existed in 1918. In the military conflict that ensued, the Baltic-German Landeswehr were defeated by the advancing Estonian Army in Northern Latvia near the city of Cēsis in June 1919. (June 23, the anniversary of the Battle of Wenden (Võnnu in Estonian) is celebrated in Estonia as a national holiday "Victory Day.")
Although Estonia had been liberated the Bolsheviks were still active and the Estonian high command decided to push their defence lines across the border into Russia. The offensive began on May 13th. By now the Estonian land, naval and air forces comprised 74,500 men including a 3,000-strong White Russian Northern Corps. This had its origins back in the autumn of 1918 as a small White Russian force raised under German approval in the Pskov area, which had retreated from the Bolsheviks and joined up with Estonian National forces. The Estonian May offensive was extremely successful and the Northern Corps mobilised local population in the liberated Russian territory. On June 19th 1919 the Estonian Commander-in-Chief General Laidoner removed the White Russians from his command and they were renamed the North-Western Army. Shortly afterwards General Nikolai N. Yudenich took command.

The Bolsheviks began a counter-offensive in July 1919 which regained much ground lost during the Estonian offensive but the North-Western Army survived. With arms provided by Britain and France and supported by the Estonian army, Estonian warships and the British Royal Navy, the North-Western Army began an offensive on 28th September 1919 with the aim of capturing Petrograd. White Russian forces got as far as ten miles from Petrograd but the Bolshevik leader Leon Trotsky gathered "an army of workers and soldiers", which was able to repulse Yudenich's troops and force their retreat back into Estonia where the Estonians, fearing the consequences of accepting an armed mob, disarmed and interned them. The Bolsheviks made determined assaults on fortified positions at the Estonian frontier but exhausted themselves and a ceasefire came into effect on 3rd January 1920.

On February 2, 1920, the Peace Treaty of Tartu was signed by the Republic of Estonia and Bolshevist Russia. The terms of the treaty stated that Russia renounced in perpetuity all rights to the territory of Estonia.

Of interest is the British contribution to the struggle in the Baltic in 1918-19: 1) arrival of British naval forces in December 1918 after lobbying in London by Estonian politicians, which brought needed military equipment, training and also artillery support from Royal Navy ships; 2) protection of the Estonian left flank by naval action in the Gulf of Finland. This included the first combined air/sea assault in history, when British aircraft and torpedo boats attacked and destroyed the Bolshevik fleet in Kronstadt; 3) the British supplied equipment including tanks and "advisors" to the White Russian North-Western Army and British tank crews are said to have got closer to Petrograd in the autumn of 1919 than German Panzer crews did to Leningrad in WWII.

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The course of World War I (WWI) activated the idea of independence. WWI directly involved Latvians and Latvian territory. Courageous Latvian riflemen (latviešu strēlnieki) fought on the Russian side during this war, and earned recognition for their bravery far into Europe. During the Russian civil war (1917-1922), Latvians fought on both sides with a significant group (known as Latvian red riflemen) supporting the bolsheviks. In the autumn of 1919 the red Latvian division participated in a major battle against the "white" anti-bolshevik army headed by the Russian general Anton Denikin.

The post-war confusion was a suitable opportunity for the development of an independent nation. Latvia proclaimed independence shortly after the end of WWI – on November 18, 1918 which is now the Independence Day in Latvia. The first to recognise Latvia's independence was Soviet Russia (on August 11, 1920), which relinquished authority and pretences to Latvian nation and territory once for all times. However, future actions proved that these had been empty promises.

The international community recognised Latvia's independence on January 26, 1921, and the recognition from many other countries followed soon. In this year Latvia also became a member of the League of Nations (September 22, 1921).

World War I devastated the country. Demands for self-determination were at first confined to autonomy ("a free Latvia in a free Russia"), but full independence was proclaimed in Riga on November 18, 1918 by the People's Council of Latvia, Kārlis Ulmanis becoming the head of the provisional government. The War of Liberation that followed was a very chaotic period in Latvia's history. By the spring of 1919 there were actually three governments -- Ulmanis' government, which concluded an agreement with the Germans and was supported by Great Britain; the Iskolat led by Pēteris Stučka, which proclaimed an independent Soviet Latvia and whose forces, supported by the Red Army, occupied almost all of the country; and the Baltic German puppet government headed by Andrievs Niedra. Estonian and Latvian forces defeated the Germans at the Battle of Cēsis in June 1919, and a massive attack by a German and Russian force under Pavel Bermondt-Avalov was repelled in November. Eastern Latvia was cleared of Bolshevik forces by Polish, Latvian, and German troops in early 1920.