TDFR Republic Day, celebrates the declaration of independence of the First Republic of Armenia and the Azerbaijan Democratic Republic from the Transcaucasian Democratic Federative Republic in 1918. (Azerbaijan and Armenia)

The Transcaucasian Democratic Federative Republic was a short-lived state in the Caucasus that included most of the territory of the present-day Armenia, Azerbaijan and Georgia, as well as parts of Russia and Turkey. The state lasted only for a month before Georgia declared independence, followed shortly after by Armenia and Azerbaijan.

The First Republic of Armenia, officially known at the time of its existence as the Republic of Armenia, was an independent Armenian state that existed from May 1918 to 2 December 1920. It encompassed roughly 10% of the Armenian highlands, primarily those under the former Russian Empire — known as Eastern Armenia — but also included some areas previously under the former Ottoman Empire — known as Western Armenia. The republic was established in May 1918, with its capital in the city of Yerevan, after the dissolution of the short-lived Transcaucasian Federation. It was the first Armenian state since the Middle Ages.

The Azerbaijan Democratic Republic, also known as the Azerbaijan People's Republic, was the first secular democratic republic in the Turkic and Muslim worlds. The ADR was founded by the Azerbaijani National Council in Tiflis on 28 May 1918 after the collapse of the Transcaucasian Democratic Federative Republic, and ceased to exist on April 28, 1920. Its established borders were with Russia to the north, the Democratic Republic of Georgia to the north-west, the Republic of Armenia to the west, and Iran to the south. It had a population of around 3 million. Ganja was the temporary capital of the Republic as Baku was under Bolshevik control. The name of "Azerbaijan" which the leading Musavat party adopted, for political reasons, was, prior to the establishment of the Azerbaijan Democratic Republic in 1918, exclusively used to identify the adjacent region of contemporary northwestern Iran.