In the early 1980s, some of the campesinos who had been active in the 1970s mobilization allied with guerrilla forces in Usulután, Tenancingo, and other contested areas of the countryside. A few, mostly younger men, became full-time fighters, others gave logistical and intelligence support. Together their support was sufficient to underwrite the FMLN's expansion from strongholds in Morazán and Chalatenango to a broad swathe of national territory, including significant areas of Usulután, by the end of 1983. While the provision of supplies and the movement of ordnance were important, the provision of military intelligence concerning the movement of government forces was the essential campesino contribution to this expansion and thus to the emergence of a military stalemate by the end of 1983. As a result, large areas of the countryside exhibited dual sovereignty by the mid 1980s. In some, state authority had been effectively replaced by novel insurgent institutions. In others, government and insurgent forces contested the authority to rule.

As insurgent forces expanded their activities in 1982 and 1983, the government changed its strategy toward winning the “hearts and minds” of residents of contested areas while intensifying the use of force in FMLN “controlled” areas.