During the messy break-up of the Soviet Union, as Armenia and Azerbaijan struggled for self-determination, Nagorno-Karabakh emerged as a breakaway region.
Nagorno-Karabakh is an ethnically Armenian enclave within the territory of Azerbaijan, internationally recognised as Azerbaijani territory. But the people of Nagorno-Karabakh want to govern themselves or to join Armenia, as they once voted to do.
A brutal war over this finally ended with a ceasefire in 1994 after the deaths of more than 30,000 people. But in the intervening 30 years, little has been done to resolve the status of Nagorno-Karabakh and there have been periodic military skirmishes between the two sides.
This one that has broken out is the most serious that there has been to date.
So why are Armenia and Azerbaijan fighting over the disputed Nagorno-Karabakh region? Al Jazeera’s Bernard Smith explains.
This video was produced and edited by Al Jazeera Newsfeed’s Katya Bohdan.