Armenia declared independence from the Transcaucasian Democratic Federative Republic, along with Azerbaijan, on May 28, 1918, to become the Democratic Republic of Armenia. (Georgia declared its independence from the Transcaucasian Federation on May 26, 1918.)
The birth of the Democratic Republic of Armenia (also known as the First Republic of Armenia) followed the battles of Sardarapat, Karakilisa and Abaran, and at a time when the situation was dire: in the territory of Armenia, there were many refugees (who escaped from the Ottoman Empire), the threat of starvation and numerous unresolved issues with its neighbors — with Turkey, in particular.
The first prime minister of the Democratic Republic of Armenia was Hovhannes Katchaznouni and the chair of the Armenian National Council was Avetis Aharonyan.
The First Republic lasted till Dec. 2, 1920, when Armenia gave way to communist power. Soon, the Armenian Soviet Socialist Republic was proclaimed, which lasted till 1991, when the Soviet Union collapsed and Armenia was again an independent state.
Today Armenia celebrates May 28 as Republic Day.