The story in 100 words
Nagorno-Karabakh is part of Azerbaijan, but its population is majority Armenian. As the Soviet Union collapsed in the 1980s, Nagorno-Karabakh voted to become part of Armenia – sparking a war which stopped with a ceasefire in 1994.
Since then, Nagorno-Karabakh has remained part of Azerbaijan, but is controlled by separatist ethnic Armenians backed by the Armenian government. Negotiations over decades, mediated by international powers, have never yielded a peace treaty.
Armenia is majority Christian while oil-rich Azerbaijan is majority Muslim. Turkey has close ties to Azerbaijan, while Russia is allied with Armenia – although it also has good relations with Azerbaijan.
The story in 500 words
Modern-day Armenia and Azerbaijan both became part of the Soviet Union when it was formed in the 1920s. Nagorno-Karabakh was an ethnic-majority Armenian region, but the Soviets gave control over the area to Azerbaijan authorities.
The Armenians in Nagorno-Karabakh made several calls to be transferred to Armenian authority control in the following decades. But it was only as the Soviet Union began to collapse in the late 1980s that Nagorno-Karabakh’s regional parliament officially voted to become part of Armenia.
Azerbaijan sought to suppress the separatist movement, while Armenia backed it. This led to ethnic clashes, and – after Armenia and Azerbaijan declared independence from Moscow – a full-scale war.