Standard, humongous, leftist volume, "Power in the Isthmus: a Political History of Modern Central America, by James Dunkerley. Author of other volumes on El Salvador, Grenada, published by Verso in the 80's and numerous articles in NLR, some relatively recent collected in, "Political Suicide in Latin America, " a highlight there being the review of Vargas Llosa novel on Peruvian Trotskyists.
In that biblio. I'd recommend the Tom Barry and Richard Millett. Milett wrote the standard work on Somoza's National Guard.
-- Michael Pugliese