Simplify the following text for a Grade 15 native English-speaking person.
Original: In June 1991 , he co-founded and commanded , alongside Hovsep Hovsepyan , the `` Liberation army '' military organization whose goal was to preserve the self-determination and defense of the local Armenian population of Nagorno-Karabakh .
Simplified: In June , 1991 , with Hovsep Hovsepyan co-founded and commanded the `` Liberation army '' military organization whose goal was to preserve the self-determination and defense of the local Armenian population of Nagorno-Karabakh .