The Red Army takes Baku in April 1920, Yerevan by December, and Tbilisi in February–March 1921, ending the independent republics. The treaties of Moscow and Kars (1921) fix the Soviet–Turkish frontier — including Nakhchivan's status as an exclave under Azerbaijani protection — in the form it still holds.
Why it mattersConquest stored the national questions rather than answering them, and the Kars settlement drew the Armenia–Türkiye–Nakhchivan geometry that the corridor diplomacy of the 2020s is still negotiating around.