On April 30, 1975, seven tanks crashed through the gates of the presidential palace in Saigon - then the capital of South Vietnam - putting an end to the Vietnam war.  Roughly 30 years later, the war is still the subject of sometimes heated debate. 

Young U.S. soldiers who were not born when the Vietnam war ended 30 years ago, fight today in Iraq and Afghanistan.  Yet the ghosts of Vietnam haunt the battlefields of Iraq and Afghanistan, as well as the corridors of power in Washington.
George Herring, author of Vietnam: America's Longest War, says Vietnam continues to affect decisions about war, peace, and politics in the United States.

"The war is not over in the sense that the issues are not resolved yet,? he said.  ?We have not resolved the issues of whether it was a good war or a bad war, or could it have been won or was lost by the foolishness of our leaders or opposition at home.  The issues are still out there.  That was so clearly evident in the [presidential] campaign back last fall."

The cold, stark numbers only hint at the tragedy the war wrought in Vietnam and the tumult it caused as it ripped American society apart: 58,000 American soldiers killed and anywhere between one and two million Vietnamese deaths.

When France tried to reassert control over its colonies in Indochina after WWII, Vietnam became a proxy conflict of the Cold War.  In 1950, the United States began helping the French with military aid, but the army of communist leader Ho Chi Minh dealt the French a crushing blow at the battle of Dien Bien Phu in 1954.  A peace conference drew what was supposed to be a temporary border between a communist North Vietnam and a non-communist South.

U.S. involvement deepened, but in the early 1960s that involvement was still minimal.  By 1964, after Democratic President Lyndon Johnson had taken office, fewer than 150 Americans had died in Vietnam.  But in 1964, President Johnson won Congressional support for greater involvement in Vietnam.  He started bombing North Vietnam and committed U.S. combat troops.  At the height of the war, there were more than 500,000 U.S. soldiers in Vietnam.

Journalist and historian Stanley Karnow, author of Vietnam: A History, points out that Lyndon Johnson had deep misgivings even as he escalated the conflict.

"Many of the tapes that have come out since then indicate that he was tormented.  There are particularly conversations with Senator Russell about, 'What am I doing here, how can I get out, how can I avoid it?'  But, on the other hand, you know, he did not want to be the first president to lose a war, he did not want to be a president to lose a war to communism," Mr. Karnow noted.

Domestic opposition to the war also escalated as the casualties increased, creating deep divides in American society.  The U.S. government had greatly underestimated the tenacity of its foe. 

The 1968 Tet offensive was a military disaster for the communists, but an even worse public relations disaster for the United States as it undercut Johnson Administration claims that the war seemed to be going well for the United States.  Anti-war demonstrations spread.

In 1968, President Johnson announced peace negotiations with North Vietnam.  And, in a stunning surprise, he said he would not run for re-election.  "I shall not seek and I will not accept my party's nomination for another term as your president," he announced.

Mr. Johnson's successor, Republican Richard Nixon, found the going in Vietnam just as tough.  He gradually decreased U.S. troops levels in Vietnam while arming and training South Vietnamese forces. 

Mr. Herring, the historian, says Mr. Nixon and his national security advisor, Henry Kissinger, thought that they could succeed where President Johnson had failed.

"Even Nixon in 1969, Nixon and Kissinger, facing obviously what was far and away the worst situation of anyone who had inherited Vietnam, somehow managed to convince themselves that they could get the sort of settlement they wanted - which meant an independent, non-communist Vietnam - if they just did things differently than the administration before them, which in this case, of course, was the Johnson administration," Mr. Herring explained.

But the U.S. invasion of Cambodia in 1970 to cut off North Vietnamese supply lines sparked massive campus demonstrations.  Four students were killed by National Guardsmen at Kent State University in Ohio.

In 1973, the United States, South Vietnam, North Vietnam, and the Viet Cong reached an agreement that ended U.S. involvement.  Mr. Nixon, already under fire for the Watergate affair that would force his resignation the following year, turned his attention elsewhere. 

Without direct U.S. military backing, the South Vietnamese government collapsed in 1975 in the face of the North Vietnamese military pressure.

The Vietnam war still hung like a cloud over U.S. military doctrine.  As Mr. Karnow says, from the end of Vietnam until the first Gulf War, U.S. military involvements have been small-scaled and short-termed.

"When we come out of the war, the motto becomes, 'never again,' let's not get involved in another situation.  So we furtively go into things like Grenada or Panama, but very, very cautiously.  When in 1983, for example, when the Marine barracks was blown up in Beirut, President Reagan withdrew the Marines.  Now in Vietnam, if that had happened during the Vietnam years, we would have reinforced the Marine barracks instead of withdraw," he explained.

The first Gulf War in 1991 caused many U.S. military and political leaders to proclaim that the rapid victory in that war marked an end to the caution that marked much of U.S. military and political foreign policy in the post-Vietnam era.  Then-President George H.W. Bush exclaimed that the United States had "shaken the Vietnam syndrome."  But debate still goes on about whether that was a premature judgment.