The correct answer is - Nagorno Karabakh.
The Armenians and the Azeris had a lot of tension between them, and it was mainly based on territorial ambitions, and which country was considering what as right.
The tensions and minor conflicts between the two nations, eventually turned into a war over the Nagorno Karabakh autonomous region in Azerbaijan. The majority of the people living in Nagorno Karabakh are of Armenian ethnicity, and the region wanted to either gain independence, or be united with Armenia. So the Armenians and the people from Nagorno Karabakh waiged a war against Azerbaijan for 14 years, from 1980 to 1994, with the outcome being a status quo situation, and two heavily exhausted nations, economically and military.