In February 1946 the Chinese Nationalists agreed to withdraw from northern Vietnam and allowed the French to return, in exchange for French concessions in Shanghai and other Chinese ports. In March Ho Chi Minh agreed to permit French troops to return to Hanoi temporarily in exchange for French recognition of his Democratic Republic of Vietnam. Chinese troops then departed. From May to September Ho Shi Minh stayed in Paris, trying to negotiate full independence and unity for Vietnam, but failed to obtain any guarantee from the French. In June the French high commissioner for Indochina, Georges Thierry d'Argenlieu, proclaimed a separatist French-controlled government for South Vietnam. After a series of violent clashes with Viet Minh, French forces bombarded Haiphong harbor and occupied Hanoi, forcing Ho Chi Minh and his Viet Minh forces to fall back to guerilla tactics. In December 30,000 Viet Minh members launched their first large-scale attack against the French, marking the beginning of an eight year struggle known as the First Indochina War.
In March Emile Bollaert replaced Admiral Thierry d’Argenlieu as French High Commissioner for Indochina. From October to December the French Operation Lea was carried out, a series of attacks on Viet Minh guerrilla positions in North Vietnam near the Chinese border. Although the Viet Minh suffered over 9000 causalities, most of the 40,000 strong Viet Minh force slipped away through gaps in the French lines.
In June 1948 French High Commissioner for Indochina, Emile Bollaert and Bao Dai, representing Vietnam, signed Halong Bay Agreement, in which France recognized the independence of Vietnam, at the same time retaining control over foreign relations and the Army of Vietnam and deferred transference of other government functions to future negotiations.
Bao Dai officially became the president of Vietnam. In July the French established the Vietnamese National Army. In October 1949 Mao Zedong defeated in China the forces of Chiang Kai-shek's Nationalist Army in the Chinese civil war, igniting American anti-Communist sentiment regarding also Vietnam
People's Republic of China and Soviet Union recognized Ho Shi Minh's Democratic Republic of Vietnam. Then the Chinese begun transferring military equipment and advisors to Viet Minh. This equipment, mostly made in USA previously belonged to Chinese nationalists, defeated by Mao. Using the Chinese help, Viet Minh's military commander, general Vo Nguyen Giap converted his guerillas into regulars. His military forces consisted of 5 light infantry divisions and one heavy division. In February United States and Great Britain recognized the Republic of Vietnam and Bao Dai's government. At the same time Viet Minh started an offensive against French outposts along the Chinese border. In USA senator McCarthy begun his "communist hunt", with great impact on American politics, also the foreign policy, including Vietnam.
In June the Corean War started.
In July president of the USA, Harry Truman authorized military aid for the French forces in Vietnam in height of 15 million Dollars. In the next 4 years USA did spend 3 billion Dollars for the support of the French war, and by 1954 did provide 80% of all war supplies used by the French. In September general Giap started attacking French outposts along the Chinese border. Their defeat cost the French 6000 people and large quantity of military equipment. At the end of September in Saigon the Americans organized Military Assistance Advisory Group (MAAG) for the French forces.
In January 20 000 Viet Minh's soldiers under general Giap started series of attacks on fortified French positions in the Red River (Song Hong/Song Ha) delta, extending from Hanoi to the Gulf of Tonkin. The open plains of delta allowed the French under general Jean de Lattre to strike back from the so-called de Lattre line, devastating the Viet Minh. 6 000 Vietnamese soldiers died during the attack on Vinh Yen near Hanoi, forcing Giap to withdraw. In march the Vietnamese attempted another attack on the outpost of Mao Khe in the vicinity of Haiphong, but were forced to withdraw under naval and aerial bombardment. The Vietnamese lost 3 000 dead. At the end of May/beginning of June Giap started yet another attempt to break through the de Lattre line, this time in the region of Day river. French reinforcements together with strikes of aircraft and armed boats resulted in another defeat for Giap, with 10 000 dead and wounded Vietnamese losses. Among the French causalities was Bernard de Lattre, the only son of General De Lattre. In June Viet Minh withdrew from the Red River delta. In September general De Lattre traveled to Washington seeking more aid from the Pentagon. In November general de Lattre left Vietnam stricken by a fatal disease - cancer - and was replaced by general Raoul Salan. In December general Giap begun a careful counter-offensive by attacking the French outpost at Tu Vu on the Black River (Song Da). He dropped conventional tactics in favor of quick hit and run attacks followed by a retreat into the dense jungles, aiming to cut French supply lines. By the end of the year, French causalities in Vietnam surpassed 90,000.
In January the Viet Minh succeeded in cutting the French supply lines along the Black River. In February the French withdrew from Hoa Binh back to the de Lattre line covered by heavy artillery barrage. For each side casualties surpassed 5000. In October general Giap once more attacked the French in the Red River delta, this time using guerilla tactics. To counter this threat, general Salan started operation Lorraine, targeting Viet Minh's supply bases in the vicinity of Viet Bac, which resulted in capturing sizeable quantities of Viet Minh equipment, but French forces failed to make contact with the enemy, so a retreat was ordered. While retreating French forces were ambushed near Chang Muong, disorganizing the retreat and causing 1200 losses of dead, wounded and captured. Operation Lorraine proved that the Vietnamese forces were increasingly better organized and were becoming extremely tough opponent in remote regions, far from main French force.
Dwight D. Eisenhower was inaugurated as the 34th U.S. President. During his presidency he greatly increased the American military assistance to the French to contain the communist expansion in southeast Asia. To justify growing expenses, Eisenhower cited the "Domino Theory" in which a communist victory in Vietnam would cause countries in the region to fall like a "falling row of dominoes". The "Domino Theory" was used by succession of presidents and their advisors to justify American involvement in the region.
In April, lack of success in attacks against French positions caused general Giap to change his strategy and invade Laos, where the forces of French Union were not as strong.
In July an armistice ended the Korean War, dividing the country at the 38th parallel into Communist North and Democratic South. The armistice was seen by many in the international community as a potential model for resolving the ongoing conflict in Vietnam.
In November French forces, under the new command of general Henri Navarre, begun operation Castor - establishing series of fortified emplacements around an old, Japaneese-built airstrip, in order to control the movement of Viet Minh forces toward Laos. General Giap immediately started concentrating his forces in the region, sensing an opportunity to strike a decisive blow against the French, who, aware of Giap's intentions, started concentrating their own troops and artillery, but have grossly underestimated Viet Minh's strength.
March 13, the decisive battle of Dien Bien Phu has begun. Heavy artillery fire caused the French to loose the possibility to use the airstrip after only two days, leaving them dependent on airdrops for supplying the base. Viet Minh begun building a maze of tunnels and trenches as a way of approaching the French positions. At the end of the month Dien Bien Phu was effectively under siege - the French run out of water and medical supplies, 10 000 French soldiers were encircled by 45 000 Viet Minh's. The French called for help from the USA, who, for some time even considered using tactical nuclear weapons. At 7th of May the French surrendered. Their losses amounted 1500 dead, the Vietnamese loose 8 000 men. The French survivors were forced to march to prison camps 500 miles away. Nearly half of them died underway or in captivity. France proceeded to withdraw completely from Vietnam, ending a bitter eight year war against the Viet Minh in which 400,000 soldiers and civilians from all sides have died.
In May the Geneva Conference on Indochina begun, attended by USA, Great Britain, China, Soviet Union, France, Vietnam (Viet Minh and representatives of Bao Dai), Cambodia and Laos, meeting to negotiate a solution for Southeast Asia.
In June a French military unit, Group Mobile 100 was decimated in series of ambushes along Road 19, between Pleiku and An Khe.
As a result of Geneva Conference in July Commanders-in-Chief of the French Union Forces and People's Army of Vietnam signed the Geneva Agreements. According to them a military demarcation line along the 17th parallel divided the fighting forces was set up and liberation of all prisoners of war and civilian internees detained by each of the two parties was appointed. The agreements forbade the introduction of any troops reinforcements, additional military personnel or reinforcements of other war material into Vietnam. War materiel destroyed, damaged, worn our or used up after the cessation of hostilities might be replaced on a piece for piece basis of the same type / characteristics. The establishment of new military bases throughout Vietnam territory was also prohibited. The application of the agreements was supervised by the International Commission consisting of representatives of India (head of Commission), Canada and Poland. Diem's government did not sign the agreement. An unsigned Final Declaration appointed general elections to reunify Vietnam to be held in July 1965. The USA opposed the unifying elections, fearing a likely victory by Ho Chi Minh, who, in October, following the French departure from Hanoi, returned after spending eight years hiding in the jungle and formally took control of North Vietnam.
In the South, Bao Dai installed Ngo Dinh Diem as his prime minister. USA put their hopes for democratic Vietnam in the anti-Communist Diem. The new prime minister was a Roman Catholic while most of the Vietnamese people were Buddhists. He encouraged Vietnamese Catholics living in Communist North Vietnam to flee south, and nearly one million of them left. At the same time about 90 000 Communists moved north, but about 10 000 Viet Minh fighters were instructed by Hanoi to quietly remain behind. From the very beginning of his government, Diem had problem with lack of popular support and even attempts of his assassination. At the end of the year, even the support of the USA for Diem was beginning to decrease.