In September 1981 , Roberto D'Aubuisson formed a new right-wing political party , known as the Nationalist Republican Alliance ( Arena ) , to combat the FMLN . One of the most violent markers of the civil war was the El Mozote massacre , in which nearly 1,000 civilians were killed during a military counterinsurgency operation . The decade would continue to see violent clashes between the opposing parties
El Mozote massacre
El Mozote massacre
Truth Commission for El Salvador