Julia Alvarez fictionalizes and retells the true story of the Mirabal sisters and their role in the revolutionary activities that eventually led to the overthrow of the Trujillo regime in the Dominican Republic. Indeed the sisters had enough popularity in the country that after they were reported to have been murdered by the regime in 1960, the rising revolutionary ferment boiled over until Trujillo himself was assassinated about six months later (about two years after the June 14, 1959, invasion discussed below). Inside the revolutionary movement, the sisters were known as the "butterflies" because this was Minerva's codename. The particular part of the movement involving the Mirabal sisters, Manolo, and other characters in the novel became known as the Fourteenth of June Movement.
The revolutionary impulse had already existed prior to June 14, 1959, when armed revolutionaries from outside the country were repelled by the regime, but this conflict is what gave the Mirabal sisters’ movement its name. Almost exactly ten years earlier, on June 19, 1949, exiled Dominicans had tried to overthrow Trujillo’s dictatorship by landing on Luperón bay by Puerto Plata, but they had failed. In 1959, another attempt to topple the regime was launched from Cuba. (Internet sources are rather unreliable, sometimes conflating the 1949 and 1959 events, and sometimes conflating the 1959 invaders with the later Fourteenth of June domestic revolutionary group.)
In a May 5, 1959, FBI record (FBI record 2-1423-9TH NR 36), it was reported that "During the past few days we have received information from three substantial sources that invasion of Cuba from Dominican Republic is imminent. The sources are: (1) General Manuel Benitez, head of National Police of Cuba from 1940 to 1944 and member of Cuban Legislature from 1948 to 1958; (2) Frank Perez Perez, a source of Miami Office who is aligned with General Benitez and Rolando Masferrer, former Cuban Senator and newspaperman who maintained a private army of hoodlums while Batista was in power and who has been described as a bandit and gangster; (3) I. Irving Davidson, registered agent of Israeli and Nicaraguan Governments who talked with Batista in the Dominican Republic on 4/29/59 and who quotes Batista as stating a group of Cuban riffraff is planning invasion of Cuba from the Dominican Republic with approval of Generalissimo Trujillo who feels Castro will attack if not attacked first."
Castro did help a revolutionary force attack first, about a month later. The attack on June 14 and June 20, 1959, came on three fronts, by both land and sea. Richard Lee Turits in Foundations of Despotism reports that the fighters were Dominican exiles and other revolutionaries from Cuba and elsewhere in Latin America. These members of the Dominican Liberation Movement had trained in Cuba for about three months. The air landing in Constanza, in the middle of the country, involved several dozen rebels. They were dressed in Dominican Air Force uniforms and fought Trujillo’s forces in the nearby mountains.
On July 6, 1959, Time Magazine reported: "'If aggressors want to see their beards and brains flying like butterflies, let them approach the shores of the Dominican Republic,' warned Dictator Rafael Leonidas Trujillo. A pair of Cuba-based rebel invasion forces—one of 63 men arriving by C46 at the mountain-ringed, mid-island town of Constanza, and another of 150 aboard two Chris-Craft launches that landed near Puerto Plata on the north coast—put the strongman's boast to the test of arms. Last week, both by government and rebel account, Trujillo proved that he meant what he said." (emphasis added)
Indeed, as for the Puerto Plata attack, Turits argues that they maintained loyalty to the regime and chose to defend it rather than help the rebels. Turits notes that the peasants of other, disaffected areas, such as Monte Plata, might have been more likely to help. As Time reported, "the government countered rebel claims of a successful landing with a communiqué full of gore. The 'liberators' who survived an air and naval bombardment, it said, 'waded ashore apparently hoping still to march on Ciudad Trujillo with the aid of peasants. It did not work that way. Machete-swinging farmers beat government troops to the beach. The invasion ended in a murderous flailing of razor-sharp machetes on the reddened sands. Army patrols found only dismembered bodies.'"
Trujillo used the occasion to start modernizing his military capabilities, and he awarded medals to the successful soldiers which read, “Constanza Heroismo y Lealtad.” Cuba ended diplomatic relations with the Dominican Republic and tried to drum up United Nations support for the rebels.
As for the domestic revolutionaries, the failed invasion had a catalyzing effect. The revolutionary group in Puerto Plata, led by Manolo Tavarez Justo and Minerva Mirabal Reyes, gave themselves the name “El Movimiento 14 de Junio” or “The Fourteenth of June Movement,” or “J14” for short. While the peasants of Puerto Plata had failed to help the invading forces as expected, Turits notes that the revolutionaries consisted mainly of the country’s new middle class of young professionals and merchants, as well as university students. The movement was, understandably, banned, and the assassination of its leaders only caused more and more revolutionary ferment in the country.