The four objectives of the operation (which evolved over time) were to boost the sagging morale of the Saigon regime in the Republic of Vietnam, to persuade North Vietnam to cease its support for the communist insurgency in South Vietnam without actually taking any ground forces into communist North Vietnam, to destroy North Vietnam's transportation system, industrial base, and air defenses, and to cease the flow of men and materiel into South Vietnam. Attainment of these objectives was made difficult by both the restraints imposed upon the U.S and its allies by Cold War exigencies and by the military aid and assistance received by North Vietnam from its communist allies, the Soviet Union and the People's Republic of China (PRC).