Title: Empire of Vietnam
Content:  During World War II, after the fall of France and establishment of Vichy France, the French had lost practical control in French Indochina to the Japanese, but Japan stayed in the background while giving the Vichy French administrators nominal control. This changed on 9 March 1945 when Japan officially took over. To gain the support of the Vietnamese people, Imperial Japan declared it would return sovereignty to Vietnam. Emperor Bảo Đại declared the Treaty of Huế made with France in 1884 void. Trần Trọng Kim, a renowned historian and scholar, was chosen to lead the government as prime minister.
Title: First Indochina War
Content:  home in France, Bảo Đại appointed Ngô Đình Diệm as Prime Minister of South Vietnam. With American support, in 1955 Diem used a referendum to remove the former Emperor and declare himself the president of the Republic of Vietnam. When the elections failed to occur, Việt Minh cadres who stayed behind in South Vietnam were activated and started to fight the government. North Vietnam also invaded and occupied portions of Laos to assist in supplying the National Liberation Front guerrillas fighting in South Vietnam. The war gradually escalated into the Second Indochina War, more commonly known as the Vietnam War in the West and the American War in Vietnam.
Title: Vietnam
Content:  from 111 BC, until the first independent dynasty emerged in 939. Successive monarchical dynasties absorbed Chinese influences through Confucianism and Buddhism, and expanded southward to the Mekong Delta. The Nguyễn—the last imperial dynasty—fell to French colonisation in 1887. Following the August Revolution, the nationalist Viet Minh under the leadership of communist revolutionary Ho Chi Minh proclaimed independence from France in 1945. Vietnam went through prolonged warfare through the 20th century. After World War II, France returned to reclaim colonial power in the First Indochina War, from which Vietnam emerged victorious in 1954. The Vietnam War began shortly after, during which the nation was divided into communist North supported by the Soviet Union and China, and anti-communist South supported by the United States. Upon North Vietnamese victory in 1975, Vietnam reunified as 
Title: First Indochina War
Content:  it as a Federation of Associated States. In 1949, they put former Emperor Bảo Đại back in power, as the ruler of a newly established State of Vietnam. The first few years of the war involved a low-level rural insurgency against the French. In 1949 the conflict turned into a conventional war between two armies equipped with modern weapons supplied by the United States, China and the Soviet Union. French Union forces included colonial troops from their former empire - Moroccan, Algerian, and Tunisian Arabs/Berbers; Laotian, Cambodian and Vietnamese ethnic minorities; Black Africans - and French professional troops, European volunteers, and units of 
Title: Vietnam War
Content:  The Vietnam War (Chiến tranh Việt Nam), also known as the Second Indochina War, was a conflict in Vietnam, Laos, and Cambodia from 1 November 1955 to the fall of Saigon on 30 April 1975. It was the second of the Indochina Wars and was officially fought between North Vietnam and South Vietnam. North Vietnam was supported by the Soviet Union, China, and other communist allies; South Vietnam was supported by the United States, South Korea, the Philippines, Australia, Thailand, and other anti-communist allies. The war, considered a Cold War-era proxy war by some, lasted almost 20 years, with direct U.S. involvement ending in 
Title: Western imperialism in Asia
Content:  France remained determined to retain its control of Indochina. However, in Hanoi, in 1945, a broad front of nationalists and communists led by Ho Chi Minh declared an independent Republic of Vietnam, commonly referred to as the Viet Minh regime by Western outsiders. France, seeking to regain control of Vietnam, countered with a vague offer of self-government under French rule. France's offers were unacceptable to Vietnamese nationalists; and in December 1946 the Việt Minh launched a rebellion against the French authority governing the colonies of French Indochina. The first few years of the war involved a low-level rural insurgency against French authority. However, after the Chinese communists reached the Northern border of Vietnam in 1949, the conflict turned into a conventional war between two armies equipped with modern 
Title: History of French foreign relations
Content:  Vietnam (DRV). The DRV ruled as the only civil government in all of Vietnam for a period of about 20 days, after the abdication of the "Japanese puppet", Emperor Bảo Đại. On 23 September 1945, French forces overthrew the local DRV government, and declared French authority restored in Cochinchina. Guerrilla warfare began around Saigon immediately. The first few years of the war involved a low-level rural insurgency against French authority. However, after the Chinese communists reached the Northern border of Vietnam in 1949, the conflict turned into a conventional war between two armies equipped with modern weapons supplied by the United States and 
Title: Empire of Vietnam
Content:  The Empire of Vietnam (Literary Chinese and Japanese: 越南帝國) was a short-lived puppet state of Imperial Japan governing the former French protectorates of Annam and Tonkin between March 11 and August 25, 1945. At the end of its rule, the empire also successfully reclaimed Cochinchina into Vietnam.
Title: Commercial Import Program
Content:  During World War II, Imperial Japan attacked Indochina and wrested control from France, but when they were defeated by the Allies in 1945, a power vacuum resulted. The communist-dominated Vietminh of Ho Chi Minh fought for Vietnamese independence, while the French attempted to regain control of their colony by creating the French Union-allied State of Vietnam. Up until 1954, the First Indochina War raged. In 1954, the French lost the Battle of Dien Bien Phu and the Geneva Conference was held to determine the future of French Indochina. The Vietminh were given control of North Vietnam, while the State of Vietnam controlled the territory south of the 17th parallel. The Geneva agreements, which the 
Title: First Indochina War
Content:  Red River Delta, 4,800 French troops had been killed, captured or missing in action and 2,000 wounded out of a total garrison force of over 10,000. Also lost were 13 artillery pieces, 125 mortars, 450 trucks, 940 machine guns, 1,200 submachine guns and 8,000 rifles destroyed or captured during the fighting. China and the Soviet Union recognized Hồ Chí Minh as the legitimate ruler of Vietnam and sent him more and more supplies and material aid. The year 1950 also marked the first time that napalm was ever used in Vietnam (this type of weapon was supplied by the U.S. for the use of the French Aéronavale).

Question: who was the first imperial power that was fighting in vietnam?
Answer: France.