Because Somoza refused to improve his human rights policies in the 1970s,

The Carter administration pressured Nicaraguan dictator Anastasio Somoza to improve his human rights record, but he refused. As Somoza’s rule collapsed in 1979 and the Sandinistas took power, the United States did not intervene militarily to save his regime. Mujahideen forces were associated with Afghanistan, not Nicaragua, and neither a U.S. invasion nor a U.N. peacekeeping mission occurred.

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