Answer
Actually, the true reason that the US was involved in the war in Nicaragua is because the democratically elected Nicaraguan President, Ortega, was not giving in to US economic demands. Therefore, the Fascist US sided with the Right Wing extremists, The Contras.
One more thing, according to Kagan, the ostensible goal of U.S. support for the contras, according to some in the Administration, was not to overthrow the Sandinistas but to compel them to stop sending arms to the Salvadoran rebels.
Also, the United States had limited military presence in Nicaragua, having only one patrolling U.S. Navy ship off the coast of Bluefields, in order to protect the lives and interests of American citizens who lived there. The Conservative Party sought to overthrow Zelaya which led to Estrada's rebellion in December 1909.
