Wikipedia
Carlos Fonseca is considered the principal ideologue of the Sandinistas because he established the fundamental ideas of Sandinismo, which is named after Augusto Sandino, an ardent fighter who voraciously supported anti-imperialism.
Many aspects of Sandinismo are similar to tendencies in other forms of political thought in Latin America like its appeal to the largest mass of the population and its anti-imperialist rhetoric. The most important attributes of the ideology make it solely a Nicaraguan creation. In Sandinismo there is an emphasis that revolution begins in rural regions among Nicaragua's oppressed peasantry, Sandinista ideas are rooted in the symbols of Augusto César Sandino and there is an effort to develop conscious growth through education.
Carlos Fonseca adopted many of the Sandinista military goals from Che Guevara in 1959. Just as Guevara had implemented his Guerrilla foco in the Sierra Maestra mountains of the Oriente province, Fonseca believed Nicaragua's Revolution would begin with mass insurgence in the countryside.
Fonseca's ideological tendency was entitled the "Prolonged Popular War" (GPP) because of its ideological commitment to creating an insurgency among the peasantry and its reliance on Maoist guerrilla strategy. The gradualist approach in the countryside involved isolating portions of the superiorly armed and trained National Guard into weaker portions, and eliminating these smaller segments one by one. The GPP desired popular support from the rural masses, a desire that remained illusive throughout the insurrectional years. The GPP believed that, in order to take part in guerrilla activities, peasants had to develop new 'revolutionary consciousness'.