The Armenia–Azerbaijan border (, ) is the international border between Armenia and Azerbaijan. Estimates of the border's length vary from to . European routes E002 and E117 cross the border.
The de jure border follows that of the former Armenian Soviet Socialist Republic and the Azerbaijan Soviet Socialist Republic and consists of two main segments – that between Armenia and Azerbaijan's Nakhchivan exclave in the west, and the longer section between Armenia and 'mainland' Azerbaijan to the east. Additionally, there are a number of enclaves on either side of the boundary, however these no longer exist except in a de jure sense. The border between Armenia and Azerbaijan has been closed since 1991.
Geography
Western (Nakhchivan) section
The border starts in the north at the tripoint with Turkey on the Aras river, and proceeds overland in a south-easterly direction along various mountain ridges, such as the Zangezur Mountains, down to the western tripoint with Iran on the Aras. Additionally, the Azerbaijani enclave of Karki/Tigranashen lies just north of the border, however since May 1992, following the First Nagorno-Karabakh War, Karki has been controlled by Armenia, which administers the territory as part of its Ararat Province.
Eastern section
The border starts in the north at the tripoint with Georgia and proceeds overland in a broadly south-easterly direction, zigzagging next to and around the Voskepar river, crossing through part of the Joghaz Water Reservoir at the mouth of the Voskepar, and touching the western tip of the Abbasbayli Water Reservoir. It then forms a broad concave arc along the Khndzorut Range and down to the Miapor Range. It then runs parallel with the eastern shore of Lake Sevan along the Sevan Range, runs south along the Eastern Sevan Range, and then west along the Vardenis Range before turning sharply east, thus creating an Azeri protrusion encompassing Böyük Alagöl lake. It then proceeds southwards, crossing the Aylakh-Lich Lake and Sev Lich State Sanctuary, terminating at the Iranian border on the Aras river. The entire border lies mainly in mountainous terrain, with elevations averaging between and .
Additionally, in the northern stretch of the boundary area there are four enclaves – one Armenian (Artsvashen/Başkənd) and three Azerbaijani (Sofulu, Yukhari Askipara/Verin Voskepar and Barxudarlı); since the war all four enclaves are now controlled by their 'host' nation and have for all practices purposes ceased to exist, though they are often depicted on official Armenian and Azerbaijani government maps.
History
During the 19th century the Caucasus region was contested between the declining Ottoman Empire, Persia and Russia. Over the span of the 1800s, Russia had pushed south at the expense of the Persian and Ottoman Empires. By the Russo-Persian War (1804–1813) and the subsequent Treaty of Gulistan, Russia acquired the bulk of what is now Azerbaijan and part of what is now Armenian's Syunik Province (historically known as Zangezur). Following the Russo-Persian War (1826–1828) and the Treaty of Turkmenchay Persia was forced to cede Nakhchivan and the rest of what is now Armenia.
In 1867 Russia organised its Armenian and Azerbaijani territories into the governorates of Erivan, Tiflis, Baku and Elisabethpol. Relations between Armenians and Azerbaijanis in the governorates were often tense, for example in 1905–07 there was an outbreak of ethnic violence which resulted in thousands of deaths.
Following the Russian Revolution in 1917 the peoples of the southern Caucasus had declared the Transcaucasian Democratic Federative Republic (TDFR) in 1918 and started peace talks with the Ottomans. Internal disagreements led to Georgia leaving the federation in May 1918, followed shortly thereafter by Armenia and Azerbaijan. With the Ottomans having invaded the Caucasus and quickly gained ground, the three new republics were compelled to sign the Treaty of Batum on 4 June 1918, by which they recognised the pre-1878 Ottoman-Russia border, thereby ceding most of Nakhchivan and a considerable part of western Armenia to the Ottomans. Armenia in particular was reeling from the aftermath of the Ottoman-led Armenian genocide, which had resulted in vast numbers of refugees fleeing eastern Turkey. The borders between the three new republics were all disputed. War broke out between Armenia and Azerbaijan over disputed territories along the frontier, lasting from 1918 to 1920, focussing on the disputed areas of Nakhchivan (under the control of the short-lived 'Republic of Aras'), Zangezur and Nagorno-Karabakh.