Final declaration, dated July 21, 1954, of the Geneva Conference on the problem of restoring peace in Indochina, in which the representatives of Cambodia, the Democratic Republic of Viet-Nam, France, Laos, the People's Republic of China, the State of Viet-Nam, the Union of Soviet Socialist Republics, the United Kingdom and the United States of America took part...
4. The Conference takes note of the clauses in the agreement on the cessation of hostilities in Viet-Nam prohibiting the introduction into Viet Nam of foreign troops and military personnel as well as of all kinds of arms and munitions...
5. The Conference takes note of the clauses in the agreement on the cessation of hostilities in Viet-Nam to the effect that no military base at the disposition of a foreign state may be established in the regrouping zones of the two parties...
7. The Conference declares that, so far as Viet-Nam is concerned, the settlement of political problems, effected on the basis of respect for the principles of independence, unity, and territorial integrity, shall permit the Vietnamese people to enjoy the fundamental freedoms, guaranteed by democratic institutions established as a result of free general elections by secret ballot.
In order to insure that sufficient progress in the restoration of peace has been made, and that all the necessary conditions obtain for free expression of the national will, general
elections shall be held in July 1956, under the supervision of an international commission composed of representatives of the member states of the International Supervisory Commission referred to in the agreement on the cessation of hostilities.
Modern History Sourcebook: The Final Declaration of The Geneva Conference: On Restoring Peace in Indochina, July 21, 1954
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Those elections were never held because the South Vietnamese dictatorship did not allow them to be held. The United States did not sign and did not honor that the Geneva Agreement of 1954. This is why:
"I have never talked or corresponded with a person knowledgeable in Indochinese affairs who did not agree that had elections been held as of the time of the fighting, possibly 80 per cent of the population would have voted for the Communist Ho Chi Minh as their leader."
Source: Dwight D. Eisenhower, Mandate for Change, 1953-56 (Garden City, NY: Doubleday & Compnay, Inc., 1963), p. 372.
https://www.mtholyoke.edu/acad/intrel/vietnam/ddeho.htm
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Vietnam was unimportant to American security and the U.S. economy. The United States provoked a war in which at least two million Vietnamese were killed in order to prevent the ascension of a leader the vast majority of the Vietnamese wanted. The War in Vietnam happened because the Untied States stole an election.