Armenia–Iran border

During the 19th century the Caucasus region was contested between the declining Ottoman Empire, Persia and Russia, which was expanding southwards.

[6] By the Russo-Persian War (1804–1813) and the subsequent Treaty of Gulistan, Russia acquired the bulk of what is now Azerbaijan and parts of Armenia; a border was drawn along the Aras river which is the modern border between Iran and Azerbaijan (excluding the Nakhchivan section) and Iran and Armenia.

[6][9][8] During the First World War, Russian Communists staged a successful revolution in 1917, whilst the peoples of the southern Caucasus had declared the Transcaucasian Democratic Federative Republic in 1918.

Internal disagreements led to Georgia leaving the federation in May 1918, followed shortly thereafter by Armenia and Azerbaijan.

In 1920, Russia's Red Army invaded Azerbaijan and Armenia, ending the independence of both, followed shortly thereafter by Georgia.