Operation Passage to Freedom was a term used by the United States Navy to describe the propaganda effort and the assistance in transporting 310,000 Vietnamese civilians, soldiers and non-Vietnamese members of the French Army from communist North Vietnam (the Democratic Republic of Vietnam) to non-communist South Vietnam (the State of Vietnam, later to become the Republic of Vietnam) between the years 1954 and 1955. The French and other countries may have transported a further 500,000. In the wake of the French defeat at the Battle of Dien Bien Phu, the Geneva Accords of 1954 decided the fate of French Indochina after eight years of war between the French Union forces and the Viet Minh, which fought for Vietnamese independence under communist rule. The accords resulted in the partition of Vietnam at the 17th parallel north, with Ho Chi Minh's communist Viet Minh in control of the north and the French-backed State of Vietnam in the south. The agreements allowed a 300-day period of grace, ending on May 18, 1955, in which people could move freely between the two Vietnams before the border was sealed. The partition was intended to be temporary, pending elections in 1956 to reunify the country under a national government. Between 600,000 and one million people moved south, including more than 200,000 French citizens and soldiers in the French army while between 14,000 and 45,000 civilians and approximately 100,000 Viet Minh fighters moved in the opposite direction.
The 1954–1955 Great Migration of Northerners was facilitated primarily by the French Air Force and Navy. American naval vessels supplemented the French in evacuating northerners to Saigon, the southern capital. The operation was accompanied by a large humanitarian relief effort, bankrolled mainly by the United States government in an attempt to absorb a large tent city of refugees that had sprung up outside Saigon. For the US, the migration was a public relations coup, generating wide coverage of the flight of Vietnamese from the perceived oppression of communism to the "free world" in the south. The period was marked by a Central Intelligence Agency-backed propaganda campaign on behalf of South Vietnam's Catholic Prime Minister Ngo Dinh Diem. The campaign was usually viewed to exhort Catholics to flee "impending religious persecution" under communism, and around 60% of the north's 1.14 million Catholics immigrated. The Viet Minh also tried to forcefully prevent would-be refugees from leaving, especially in rural areas where there were no French or American military forces.
The migration was conventionally supposed to boost the Catholic power base of Diem; whereas the majority of Vietnam's Catholics previously lived in the north, now most were in the south. Fearing a communist victory, Diem cancelled the elections. Believing the newly arrived Catholics to be a bastion of solid anti-communist support, Diem supposedly treated the new constituents as a special interest group. In the long run, the northern Catholics never fully integrated into Southern society and Diem's alleged favouritism toward them were often thought to cause tension that culminated in the Buddhist crisis of 1963, which ended with his downfall and assassination. In fact, Catholics moving to the South were foremost the active agents of their own lives, not because of the CIA or Ngô Đình Diệm's efforts. About 25% of the migrants were non-Catholic and a number of Catholics who moved to the South did not do so because of their religion. Northern Catholic émigrés actually brought complex challenges to the Church in South Vietnam, and Ngô Đình Diệm also did not resettle northern Catholics in and around Sài Gòn as a deliberate and strategic policy. As Vietnamese Catholics were far from monolithic, and were not in any way unified in their political stances, it is a myth to conflate "Catholic refugees with all Catholics, with all refugees or with staunch supporters of Ngô Đình Diệm". In reality, the Personalist Revolution under Diệm's regime promoted religious freedom and diversity to oppose communism's atheism. However, this framework itself ultimately enabled Buddhist activists to threaten the state that supported their religious liberty.
At the end of World War II, the Viet Minh had proclaimed independence under the Democratic Republic of Vietnam (DRV) in September 1945. This occurred after the withdrawal of Imperial Japan, which had seized control of French Indochina during World War II. The military struggle restarted in November 1946 when France attempted to reassert control over Indochina with an attack on the northern port city of Haiphong. The DRV was recognised by the Soviet Union and the People's Republic of China (PRC), while the western powers recognised the French-backed State of Vietnam, nominally led by Emperor Bảo Đại, but with a French-trained Vietnamese National Army (VNA) which was loyal to the French Union forces. In May 1954, after eight years of fighting, the French were surrounded and defeated in a mountainous northern fortress at the Battle of Dien Bien Phu. France's withdrawal from Indochina was finalised in the Geneva Accords of July 1954, after two months of negotiations between Ho's DRV, France, the PRC and the Soviet Union. Under the terms of the agreement, Vietnam was temporarily divided at the 17th parallel north pending elections in 1956 to choose a national government that would administer a reunified country.
The communist Viet Minh were left in control of North Vietnam, while the State of Vietnam controlled the south. French Union forces would gradually withdraw from Vietnam as the situation stabilised. Both Vietnamese sides were unsatisfied with the outcome at Geneva; Ngo Dinh Diem, Prime Minister of the State of Vietnam, denounced France's agreement and ordered his delegation not to sign. He stated "We cannot recognise the seizure by Soviet China . . . of over half of our national territory" and that "We can neither concur in the brutal enslavement of millions of compatriots". North Vietnamese Prime Minister Phạm Văn Đồng expressed bitterness after his Soviet and Chinese backers threatened to cut support if he did not agree to the peace terms; Dong had wanted to press home the Viet Minh's military advantage so they could lay claim to more territory at the negotiating table.
Under the accords, there was to be a period in which free civilian movement was allowed between the two zones, whereas military forces were compelled to relocate to their respective sides. All French Far East Expeditionary Corps and VNA forces in the north were to be evacuated south of the 17th parallel, while all Viet Minh fighters had to relocate to the north. The accords stipulated that civilians were to be given the opportunity to move to their preferred half of Vietnam. Article 14(d) of the accords stated that:
Any civilians residing in a district controlled by one party who wish to go and live in the zone assigned to the other party shall be permitted and helped to do so.
Article 14(d) allowed for a 300-day period of free movement between the two Vietnams, ending on May 18, 1955. The parties had given little thought to the logistics of the population resettlement during the negotiations at Geneva, and assumed the matter would be minor. Despite claiming that his northern compatriots had been "enslaved", Diem expected no more than 10,000 refugees. General Paul Ely, the French Commissioner-General of Indochina, expected that around 30,000 landlords and business executives would move south and proclaimed that he would take responsibility for transporting any Vietnamese who wanted to move to territory controlled by the French Union, such as South Vietnam. French Prime Minister Pierre Mendès France and his government had planned to provide aid for around 50,000 displaced persons. Mendes-France was sure that the FFEEC would be able to handle the work all by itself. The Americans saw the period as an opportunity to weaken the communist north.