Um, what's happening in Nicaragua?
THE Somoza Dynasty:
US-backed Adolfo Diaz (conservative) falls to the revolutionary forces (including Augusto Sandino), and the new Liberal president appoints Anastasio Somoza Garcia to head the National Guard. Sandino is given land and a small army. In 1936, Garcia takes power and his dynasty rules for the next 43 years.
The Sandinista National Liberation Front is founded in 1961, opposing the regime. It's goal: to create a socialist state. An earthquake hits in 1967, and the President helps himself to the relief aid. The FSLN attacks and kidnaps and Somoza declares a brutal counterinsurgency effort.
Carter, wanting to withdraw American involvement from foreign affairs, withdraws aid to Nicaragua until the human rights abuses are corrected. Somoza lifts the siege to get aid, and the Sandinistas attack again, this time with broader popular support. The Union for Democratic Liberation grows. As the war continues, the US is growing increasing disillusioned with the Somoza dynasty, and decide to moderate the new, inevitable government in Nicaragua. And so, the Sandinistas seize power.
The Sandinistas acted like the Marxist-Leninists they were, nationalizing sectors of the economy, reorganized the political machine. Carter, trying to prevent an alliance with Cuba and USSR, sent aid. The Sandinistas eventually did align with the other communists and started supporting rebels in El Salvador with the aid America continued to give. Carter, and later, Reagan, demanded they cease, but they didn't, so Reagan pulled the plug on aid.
The Sandinistas were not universally adored, however. A growing group of Nicaraguans disagreed with their policies. Peasants and farmers didn't like the land policies. Elites resented the repressive economic measures. The Nicaraguan Democratic Force (FDN) was formed, supported by Washington.