In 1961 Carlos Fonseca Amador, Silvio Mayorga, and Tomás Borge Martínez formed the FSLN (Sandinista National Liberation Front) with other student activists at the Universidad Nacional Autonoma de Nicaragua (UNAN) in Managua. For the founding members of the FSLN, this was not their first experience with political activism. Amador, first General Secretary of the organization, had worked with others on a newspaper "broadly critical" of the Somoza reign titled Segovia.
On 9 April 1961, Brigade 2506 personnel, ships, and aircraft started transferring from Guatemala to Puerto Cabezas. Curtiss C-46s were also used for transport between Retalhuleu and a CIA base (code-named JMTide, aka Happy Valley) at Puerto Cabezas.
The Somoza Regime, which included the Nicaraguan National Guard, a force highly trained by the U.S. military, declared a state of siege, and proceeded to use torture, extra-judicial killings, intimidation and censorship of the press in order to combat the FSLN attacks. This led to international condemnation of the regime and in 1978 the administration of U.S. president Jimmy Carter cut off aid to the Somoza regime due to its human rights violations (Boland Amendment). In response, Somoza lifted the state of siege in order to continue receiving aid.
On 10 January 1978, the editor of the Managua newspaper La Prensa, and founder of the Union for Democratic Liberation (UDEL), Pedro Joaquín Chamorro Cardenal was murdered by suspected elements of the Somoza regime, and riots broke out in the capital city, Managua, targeting the Somoza regime.
Following the riots, a general strike on 23–24 January called for the end of the Somoza regime and was, according to the U.S. State Department staff at the U.S. Embassy, successful at shutting down around 80% of businesses in not only Managua but also the provincial capitals of León, Granada, Chinandega, and Matagalpa.
On 22 August 1978 the FSLN staged a massive kidnapping operation. Led by Éden Pastora, the Sandinistan forces captured the National Palace while the legislature was in session, taking 2,000 hostages. Pastora demanded money, the release of Sandinistan prisoners, and, "a means of publicizing the Sandinista cause."After two days, the government agreed to pay $500,000 and to release certain prisoners, marking a major victory for the FSLN.
In early 1979 the Organization of American States supervised negotiations between the FSLN and the government. However, these broke down when it became clear that the Somoza regime had no intention of allowing democratic elections to take place.
The 1984 election took place on 4 November. Of the 1,551,597 citizens registered in July, 1,170,142 voted (75.41%). The null votes were 6% of the total. International observers declared the elections free and fair, despite the Reagan administration denouncing it as a "Soviet style sham".