The vanguard of the 1965 revolution, the perredeistas (members of the PRD) and other supporters of Bosch, called themselves Constitutionalists (a reference to their support for the 1963 constitution). The movement counted some junior military officers among its ranks. A combination of reformist military and aroused civilian combatants took to the streets on April 24, seized the National Palace, and installed Rafael Molina Ureña as provisional president. The revolution took on the dimensions of a civil war when conservative military forces, led by army general Elías Wessín y Wessín, struck back against the Constitutionalists on April 25. These conservative forces called themselves Loyalists. Despite tank assaults and bombing runs by Loyalist forces, however, the Constitutionalists held their positions in the capital; they appeared poised to branch out and to secure control of the entire country.

On April 28, the United States intervened in the civil war. President Lyndon B. Johnson ordered in forces that eventually totaled 20,000, to secure Santo Domingo and to restore order. Johnson had acted in the stated belief that the Constitutionalists were dominated by communists and that they therefore could not be allowed to come to power. The intervention was subsequently granted some measure of hemispheric approval by the creation of an OAS-sponsored peace force, which supplemented the United States military presence in the republic. An initial interim government was headed by Trujillo assassin Imbert; Héctor García Godoy assumed a provisional presidency on September 3, 1965. Violent skirmishes between Loyalists and Constitutionalists went on sporadically as, once again, elections were organized.