A chronology of the U.S. relationship with Vietnam:
1961: The U.S. military buildup in Vietnam begins.
May 4, 1964: Trade embargo is imposed on North Vietnam in response to attacks from the North on South Vietnam.
Aug. 2, 1964: Pentagon says North Vietnamese torpedo boats attack the U.S. destroyer Maddox in the Gulf of Tonkin.
Aug. 7, 1964: Congress approves the Gulf of Tonkin Resolution allowing the president to take any necessary measures to repel further attacks.
1965-1969: Number of U.S. troops in Vietnam grows from 60,000 to 543,000.
Oct. 21-23, 1967: In Washington, D.C., 50,000 people demonstrate against the war.
Jan. 31, 1968: The Tet Offensive. Communist forces launch attacks on Hue and other major cities, towns and military bases throughout South Vietnam. One assault team gets inside the walls of U.S. embassy in Saigon before it is repulsed.
March 16, 1968: In the hamlet of My Lai, an estimated 150 unarmed Vietnamese civilians are herded into a ditch and gunned down by members of Army Lt. William L. Calley Jr.'s platoon in what is considered the worst atrocity in the Army's history.
May 13, 1968: Direct peace talks between U.S. and Vietnamese officials open in Paris.
June 8, 1969: President Nixon announces the first troop withdrawals from South Vietnam.
Nov. 15, 1969: In Washington, 250,000 people demonstrate against the war.
1970: The draft lottery begins.
April 30,1970: American and South Vietnamese armies invade Cambodia.
May 4, 1970: Four students are killed by National Guardsmen at Kent State University in Ohio.
Jan. 27, 1973: The United States, South Vietnam, North Vietnam and Viet Cong sign the Paris Peace Accords, ending the American combat role in the war. Draft ends.
March 29, 1973: Last American combat troops leave Vietnam.
April 29, 1975: Saigon falls and last Americans are evacuated.
April 30, 1975: South Vietnam surrenders to North Vietnam ending the war and reunifying the country under communist control.
Nov. 11, 1982: Vietnam Veterans Memorial is dedicated in Washington on Veterans Day.
October 1991: Washington takes steps to normalize relations with Hanoi.
Feb. 3, 1994: President Clinton lifts trade embargo.
July 1995: The United States restores diplomatic relations with Vietnam.