Secession in 1988 led to a war that killed some 30,000 people. A shaky ceasefire ensued in 1994, with Azerbaijan losing 14% of its territory. Exchanges of fire along the front have long been common, but the clashes this year have been the worst since 1994.

http://www.economist.com/news/europe/21615631-nasty-war-seems-brink-flaring-up-again-mountainous-conflict