Original: In the final years of the Soviet Union, the region re-emerged as a source of dispute between Armenia and Azerbaijan, culminating in a large ethnic conflict and, eventually, in the Nagorno-Karabakh War that was fought from 1991 to 1994.
Simplified: In the final years of the Soviet Union, the region again became a source of dispute between Armenia and Azerbaijan, culminating in the Nagorno-Karabakh War of 1988-1994.