On April 28, U.S. President Lyndon Johnson, concerned that communists might take over the revolt and create a "second Cuba," sent 42,000 troops into Santo Domingo, in Operation Powerpack. "We don't propose to sit here in a rocking chair with our hands folded and let the Communist set up any government in the Western Hemisphere," Johnson said. The forces were soon joined by comparatively small contingents from the Organization of American States (OAS). The Loyalists used the U.S. presence to deploy its forces and attack Constitutionalists. As a result, Loyalist forces destroyed most Constitutionalist bases and captured the rebel radio station, effectively ending the war. On May 13, Loyalist forces launched  Operation Limpieza and captured the northern part of Santo Domingo. Many black civilians were killed during the operation. A cease-fire was declared on May 21.