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Although the Russian Caucasus Army of Imperial forces commanded by Nikolai Yudenich and Armenians in volunteer units and Armenian militia led by Andranik Ozanian and Tovmas Nazarbekian succeeded in gaining most of Ottoman Armenia during World War I, their gains were lost with the Bolshevik Revolution of 1917.[citation needed] At the time, Russian-controlled Eastern Armenia, Georgia, and Azerbaijan attempted to bond together in the Transcaucasian Democratic Federative Republic. This federation, however, lasted from only February to May 1918, when all three parties decided to dissolve it. As a result, the Dashnaktsutyun government of Eastern Armenia declared its independence on 28 May as the First Republic of Armenia under the leadership of Aram Manukian.

When was the Bolshevik Revolution?
1917