As a result of the Russo-Turkish war of 1877-1878, the regions of Kars, Ardahan, Artvin, and Batum, at the time in the Ottoman Empire, went to Russia.
The next conflict between Russia and the Ottoman Empire was during World War I. The Caucasian expedition of Enver Pasha in late 1914-1915 was soundly defeated in the battle of Sarikamish. Enver covered his defeat by accusing the Armenians of treason. As a result, the Armenian soldiers in the Ottoman Empire were disarmed and killed en masse, and the subsequent massacres and deportation of Armenians would soon turn into genocide. The Russian forces occupied an important section of Western Armenia (Van, Erzerum, Bitlis and Mush, Trebizond, and Erzinga) in 1915-1916.
After the October Revolution, the Russian forces abandoned the front. The Armenian battalions formed in a hurry were insufficient to stop the Ottoman advance and the territories of Western Armenia were lost between February and April 1918. The Treaty of Brest Litovsk (March 3, 1918) between Soviet Russia and the Ottoman Empire recognized the transfer of Kars, Ardahan, and Batum to the latter. After the armistice of Mudros (October 30, 1918), the Republic of Armenia established its sovereignty over most of the region of Kars, and the Treaty of Sevres recognized the region of Kars and most of Western Armenia as part of Armenia (August 1920).
However, as a result of the Armeno-Turkish war of September-November 1920, the region of Kars and Alexandropol (nowadays Gumri) was occupied by the Turkish forces, which threatened once again the existence of Armenia. The invasion of the XI Red Army on November 29 forced the government of the Republic of Armenia to transfer the authority to the Communists on December 2, which turned the country into a Soviet republic.
Meanwhile, the representatives of the Republic signed the Treaty of Alexandropol with the Turks on the night of December 2 to 3. This treaty recognized the occupation of the region of Kars by Turkey. However, its legal validity was dubious, because it had been signed on behalf of a government that was already out of office. The next step was the signature of the Treaty of Moscow between Kemalist Turkey and Soviet Russia on March 16, 1921. Turkey received the region of Kars, and the southern portion of the region of Batum. Probably as a compensation for the north of the region of Batum, the Bolsheviks transferred the Armenian province of Surmalu to the Turks.
At the time, the February rebellion had expelled the Communist government from Armenia, while Georgia was still an independent republic. After Armenia and Georgia were finally occupied by the Red Army, the signature of the Treaty of Kars was meant to confirm the terms of the Treaty of Moscow by the representatives of Armenia, Georgia, and Azerbaijan.
The treaty was signed on October 13, 1921, and ratified in Yerevan on September 11, 1922. Signatories included four Turkish representatives, Russian ambassador Yakov Ganetsky, and two representatives from Armenia, Azerbaijan, and Georgia. Minister of Foreign Affairs Askanaz Mravian and Minister of Interior Poghos Makintsian signed it on behalf of Armenia.
The treaty confirmed the division of the region of Batum, with the north ceded by Turkey to Georgia and the south, with the city of Artvin, annexed by Turkey, which was also guaranteed free transit through the port of Batum.
It also created a new boundary between Turkey and Armenia, defined by the Akhurian and Arax rivers. Turkey annexed most of the region of Kars, including Surmalu, with Mount Ararat and the cities of Igdir and Koghb, the cities of Kars, Ardahan, and Olti, and the ruins of Ani.
The region of Nakhichevan became an autonomous territory under the protection of Azerbaijan, which was turned into the Autonomous Soviet Socialist Republic of Nakhichevan in 1924, as an exclave subordinate to Soviet Azerbaijan and sharing a fifteen kilometer boundary with Turkey.
The Soviet Union attempted to annul the Treaty of Kars and regain the lost territories of Kars, Ardahan, and Artvin after World War II on behalf of Armenia and Georgia. However, British Prime Minister Winston Churchill objected to those territorial claims, and in 1947 the Soviet Union gave up its claims from Turkey.
The validity of the Treaty of Kars has been questioned on the basis that the sides that signed it did not have authority. The Turkish Grand National Assembly, which was represented by the Turkish signatories, had no authority to sign international treaties, which still rested with the legal ruler of the Ottoman Empire, the Sultan, as established by its Constitution. The Republic of Turkey was proclaimed in 1923. On the other hand, the Soviet republics were under strict control of Moscow and the Soviet Union was established in December 1922.
After the dissolution of the Soviet Union in 1991, the Treaty of Kars was accepted by Turkey, Georgia, and Azerbaijan. However, the government of Armenia has made no such ratification.