The FSLN was officially founded in Honduras on the symbolic date of July 26, 1961, the eighth anniversary of the launching of the Cuban revolution by Fidel Castro Ruz. The FSLN operated at first in the mountainous region that forms the border between Honduras and Nicaragua. Early successes were few, however, and the hardships and sheer effort of surviving led to discontent and desertions. Between 1970 and 1974, the FSLN struggled to broaden its bases of support by conducting guerrilla operations in the countryside while recruiting new supporters in the cities. Its rural guerrilla tactics were patterned after those of Castro's forces, and FSLN forces were trained in Cuba.

For many observers, the FSLN first became a force to be reckoned with when it executed a spectacular raid and hostagetaking at a reception for the United States ambassador in Managua in December 1974 (see The End of the Anastasio Somoza Debayle Era , ch. 1). The Anastasio Somoza Debayle administration was forced to accede to humiliating FSLN demands for ransom and political freedom for fourteen FSLN prisoners. The National Guard followed with a major counteroffensive that reduced armed resistance in the countryside. The FSLN remained on the defensive until 1977, but the guard's harsh reprisals caused popular feeling to swing even more toward the Sandinistas.

The seizure of the National Palace by a small group of Sandinistas in August 1978 sparked a mass uprising in the following month. The uprising was a turning point in the struggle to overthrow Anastasio Somoza Debayle. The FSLN no longer was fighting alone but rather was organizing and controlling a national insurrection of citizens eager to join the anti-Somoza movement. Hard-core Sandinista guerrillas numbered perhaps 2,000 to 3,000 untrained popular militias and foreign supporters added several thousand more to this total. Although the "first offensive" of September 1978 declined toward the end of the year, fighting did not completely stop. The FSLN mounted its "final offensive" in May 1979, capturing a number of cities in June, and launching a three-pronged assault against Managua in early July. When Anastasio Somoza Debayle, strongly urged by the United States, resigned on July 16 and fled the country, the National Guard collapsed two days later.

Data as of December 1993