Nagorno-Karabakh, officially the Nagorno-Karabakh Republic (NKR; Armenian: Լեռնային Ղարաբաղի Հանրապետություն Lernayin Gharabaghi Hanrapetut'yun; Azerbaijani: Dağlıq Qarabağ Respublikası), Artsakh Republic or Republic of Artsakh (Armenian: Արցախի Հանրապետություն Arts'akhi Hanrapetut'yun), is an unrecognised republic in the South Caucasus. The region is considered by the UN to be part of Azerbaijan, but is under the control of ethnic Armenian separatists. The NKR controls most of the territory of the former Nagorno-Karabakh Autonomous Oblast and some of the surrounding area, giving it a border with Armenia to the west, Iran to the south, and the uncontested territory of Azerbaijan to the north and east.

The predominantly Armenian-populated region of Nagorno-Karabakh was claimed by both the Azerbaijan Democratic Republic and the First Republic of Armenia when both countries became independent in 1918 after the fall of the Ottoman Empire, and a brief war over Nagorno-Karabakh broke out in 1920. The dispute was largely shelved after the Soviet Union established control over the area and created the Nagorno-Karabakh Autonomous Oblast (NKAO) within the Azerbaijan SSR in 1923. During the fall of the Soviet Union, the region re-emerged as a source of dispute between Armenia and Azerbaijan. In 1991, a referendum held in the NKAO and the neighbouring Shahumian region resulted in a declaration of independence. Large-scale ethnic conflict led to the 1991–1994 Nagorno-Karabakh War, which ended with a ceasefire that left the current borders.

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