Early contacts between the United States and Vietnam began around 1787, when US minister to France Thomas Jefferson met the exiled Vietnamese Prince Cảnh, son of the future Emperor Gia Long in Paris, as Jefferson showed interest in dry rice varieties from Cochinchina (South Vietnam).Phạm Xanh . "Những cuộc tiếp xúc Việt – Mỹ đầu tiên dưới triều Nguyễn nửa đầu thế kỷ XIX. Tạp chí Nghiên cứu Lịch sử số tháng 6 năm 1999.

In 1945, toward the end of World War II, the US Office of Strategic Services assisted the Viet Minh in gaining intelligence against the Japanese. With the emergence of the Cold War, the US supported the anticommunist, French-associated State of Vietnam against the communist-controlled Democratic Republic of Vietnam. After the dissolution of French Indochina in 1954, the US supported the anticommunist South Vietnam as opposed to communist North Vietnam and fought North Vietnam directly during the Vietnam War. After American withdrawal in 1973 and the subsequent fall of South Vietnam in 1975, the U.S. applied a trade embargo and severed ties with Vietnam, mostly out of concerns relating to Vietnamese boat people and the Vietnam War POW/MIA issue. Attempts at re-establishing relations went unfulfilled for decades, until U.S. president Bill Clinton began normalizing diplomatic relations in the 1990s. In 1994, the U.S. lifted its 30-year trade embargo on Vietnam, though other sanctions remained. While trade was allowed to flow, it was not on normal terms as Vietnamese exports to the U.S. still faced high tariffs in the range of 40%-80%. The following year, both countries established embassies and consulates. Relations between the two countries continued to improve into the 21st century.

Vietnam has pursued closer relations with the United States, especially in the geopolitical context of its territorial disputes with China in the South China Sea. However, it has also kept a balance between China and the United States. The Vietnamese public, unlike in other communist countries, has a favorable view of the U.S.Old Enemies Become Friends: U.S. and Vietnam Brookings InstitutionDespite All, Vietnam Still Likes Americans New York TimesNot Your Father's VietnamOpinion of the United States - Vietnam Pew Research Center Every U.S. president since diplomatic normalization in 1995 has visited Vietnam at least once, highlighting the importance of Vietnam in the U.S.'s growing pivot to Asia; these visits have been welcomed by the Vietnamese populace despite political differences.

Over 2.1 million Vietnamese Americans are largely immigrants who moved to the United States after the Vietnam War. They comprise nearly half of all overseas Vietnamese.Wieder, Rosalie. "Vietnamese American". In Reference Library of Asian America, vol I, edited by Susan Gall and Irene Natividad, 165-173. Detroit: Gale Research Inc., 1996.

History 19th century

The first American to visit Vietnam was Captain Jeremiah Briggs of The Fame, a commercial ship, set sail from Salem, Massachusetts and arrived at Huế on May 23, 1803. The second was US Navy Lieutenant John White, commanding the USS Franklin (1795) on a commercial trip to Vietnam. White arrived in Huế on June 12, 1819, but then proceeded to Manila after learning that the Emperor of Vietnam was absent from the city in Northern Vietnam. He and John Brown, Captain of the Marmion arrived at Saigon on October 9, 1819, and continued to stay at the city for another four months. He observed economy, political landscape, culture, and notably the rise of Minh Mạng and his anti-Western and anti-trade attitudes.

In 1829, U.S. president Andrew Jackson sent a diplomatic delegation led by Edmund Roberts on the USS Peacock to the Nguyễn dynasty to establish bilateral relations and expand trade between the two countries. The ship arrived in Vũng Lấm, Phú Yên province on 2 January 1833. The ruler of Vietnam at the time, Emperor Minh Mạng, was not eager to allow foreigners to freely enter Vietnam and engage in trade. The emperor required that Americans follow Vietnamese laws, and only allowed them to do business in Đà Nẵng, Central Vietnam. After receiving this unwelcome message, Edmund Roberts and his delegation left Vietnam. Vietnamese account for the US delegation arrival was brief:

Roberts returned to Vietnam for the second time on May 14, 1836, as his second attempt to establish relation with Minh Mang, but he succumbed to severe illness which halted his efforts. According to the ship doctor William Ruschenberger, Minh Mạng sent an emissary to Đà Nẵng to see the American delegation. The emissary demanded Roberts to deliver the President's letter to him, which was refused, due to Roberts' illness and lack of adequate interpreters. After shaking hands with the Vietnamese representative, Ruschenberger and the USS Peacock departed Vietnam for Macao. Edmund Roberts died there on June 12 before the delegation could achieve anything. Minh Mang promptly responded:

US Navy tried to intervene in Vietnam in 1845, 1850, and 1861, as it did in Japan in 1853.

World War II and emergence of Cold War

French Indochina in World War II underwent significant political changes. By 1941, Japan gained full military access across Indochina and established a fragile dual colonial rule that maintained Vichy French administration while facilitating Japanese military operations. US president Franklin D. Roosevelt insisted that France not be allowed to retake Indochina after the war, but instead proposed that it be placed under an international trusteeship. However, before his death, Roosevelt reversed his position on the trusteeship idea, largely due to British opposition.

At the end of the Pacific War in 1945, American agents of the Office of Strategic Services, led by officer Archimedes Patti, arrived in Vietnam, where they met with the Viet Minh, led by communist Ho Chi Minh. The OSS Deer Team provided the Viet Minh with training and weapons to gather intelligence against the Japanese, while the Viet Minh also provided OSS agents with shelter. Further upheavals followed World War II, including the Vietnamese civil conflicts largely incited by the Viet Minh and the French reconquest of southern Indochina, as well as the death of OSS officer A. Peter Dewey, who was shot by Viet Minh fighters. The Viet Minh claimed they mistook Dewey for a French soldier, and Ho Chi Minh reportedly apologized to the US and ordered a search for Dewey's body, though the revolutionary and historian Trần Văn Giàu reported that Dewey's body was dumped in a nearby river and was never recovered.

Ho wrote several letters to US President Harry S. Truman and Secretary of State James F. Byrnes seeking diplomatic recognition for the Democratic Republic of Vietnam (DRV). The emergence of the Cold War and desires to maintain good relations with France prompted the US not to recognize the communist-led Viet Minh government. The DRV government had no genuine intention of seeking a long-term alliance with the US, but with the Soviet Union instead. The Indochinese Communist Party had long embraced a "two-camp" worldview and regarded the United States as a leading enemy of world revolution. Following the Chinese Communist victory in 1949, the ICP worked to bring the DRV into the socialist camp.

With the outbreak of the First Indochina War, the US refused to publicly endorse French military action against the Viet Minh, but as much as the US abhorred colonialism, it detested communism even more. Several Vietnamese nationalists rallied around the former emperor Bảo Đại and worked with the French to establish the anticommunist State of Vietnam. From 1950, the United States recognized and supported the State of Vietnam against the communist-dominated DRV.

Vietnam War

In the 1954 Geneva Conference, French Indochina was dismantled and superseded by the independent states of North Vietnam, South Vietnam, Cambodia, and Laos. With the Cold War ongoing, Vietnam had been split into two opposing countries: North Vietnam, a communist state that opposed American ideals, and South Vietnam, an anticommunist state generally aligned with the US geopolitical outlook that communism needed to be contained. The two countries were divided at the 17th parallel north, not unlike the 38th parallel north that divided North Korea and South Korea in the Korean War. The Geneva Conference provided that a general election be held by July 1956 to unify Vietnam, but the agreements were neither directly accepted by the State of Vietnam nor the US, as both had opposed the partition in the first place. By July 1955, it was announced that South Vietnamese leader Ngo Dinh Diem would refuse the elections, citing concerns over communist manipulation.

The U.S. supported South Vietnam, having already supported France during the First Indochina War. The U.S. sent American military advisors to train and assist the Army of the Republic of Vietnam, and spent massive amounts of money in efforts to modernize the country; however, this created tensions between the U.S. and North Vietnam. Tensions reached a breaking point following the 1964 Gulf of Tonkin incident, when the U.S. accused the Vietnam People's Navy of attacking the USS Maddox and other United States Navy vessels on two separate occasions. While the first incident barely damaged the USS Maddox and resulted in 10 Vietnamese casualties (4 killed and 6 wounded), the second incident was contentious, and was proven to not have happened in the 2000s. However, at the time, U.S. President Lyndon B. Johnson used both incidents as justification to take any necessary retaliatory measures; the U.S. Congress promptly passed the Gulf of Tonkin Resolution, which authorized the deployment of American forces in Vietnam.

The Gulf of Tonkin incident started American involvement in the Second Indochina War, known in the Western world as the "Vietnam War". For 11 years, the U.S., South Vietnam, and their allies fought North Vietnam, the National Liberation Front, and their allies. Though the U.S. and South Vietnam used air superiority, close air support, and Central Intelligence Agency-led intelligence operations to their advantage, North Vietnam and the Viet Cong made use of guerrilla warfare, though their tactics gradually became more conventional as the war progressed. The Vietnam War was a massive undertaking for all involved: North Vietnam and the Viet Cong had around 690,000 soldiers by 1966, South Vietnam had a strength of 1.5 million soldiers by 1972, and the U.S. deployed a total of 2.7 million soldiers over the course of American involvement, peaking at 543,000 in April 1969. The U.S. spent roughly $140 billion ($950 billion in 2011) in direct expenses to South Vietnam to build infrastructure, train an army and police force, and modernize the country. Casualties and destruction caused by the war were immense, with the conflict killing between 1.3 million and 3.4 million people, a combined total of combatants and non-combatants from both sides. American society was greatly polarized by the war, which coincided with the height of the counterculture phenomenon and civil rights movement; opposition to American involvement in the Vietnam War was related to these movements, but was a major and significant movement in its own right. American sympathies toward and perspectives on Vietnam depended on political stance, and the U.S. government itself experienced divisions between pro-war and anti-war politicians.