Few years in modern history were as tumultuous as 1968. Assassinations, war, political polarization, invasions, racial tensions and uprisings dominated that time of torment.

Forty years later, people around the world are reflecting on the events of 1968. In the Czech Republic, plans are already underway to commemorate Prague Spring and the brutal Soviet invasion that crushed it.

The Vietnamese are organizing events in their homeland to highlight the fortieth anniversary of the bloody Tet Offensive, in which tens of thousands of communists struck a decisive blow against the American military presence in South Vietnam.

The student-worker rebellions in Paris in 1968 will be the subject of retrospectives, conferences, documentaries and museum exhibitions in France. In England, Ireland, Germany, Mexico and other parts of the world, the 40th anniversary of the sea changes that occurred in 1968 will be marked in various ways.

But no other nation was as thoroughly shaken by the turbulence of 1968 as the United States. As an opening salvo in January, the massive Tet Offensive in Vietnam shook the American public to the core, raising doubts about a war that most citizens had supported up until that point.

The assassination of Martin Luther King, Jr. in April and Bobby Kennedy in June snuffed out voices of idealism in a dangerously polarized land.

Protests at Columbia University in spring, the Chicago Democratic National Convention in August, not to mention the nightmarish race riots after King's assassination and the countless antiwar demonstrations throughout the year, contributed to a sense in 1968 that America was unravelling.

So much has changed, and yet so much remains the same.

Embers of political activism still glow, but there are no moral giants to unify the masses around causes of peace and social justice. Barack Obama can certainly deliver a stirring speech, but he lacks the sheer messianic power of King. Indeed, since 1968, no public figure --African American or otherwise -- has approached King in his power to articulate a more just society or unify such a wide array of people behind his noble cause.

As was the case in 1968, war still rages today. But the Iraq war is a post-Cold War conflict, far more modest in scale than Vietnam. Critics of the Iraq war insist on comparing it to Vietnam, but the two wars have little in common, except for the tragic hubris of the Washington officials most responsible for them. Vietnam was a more destructive intervention. Round-the-clock bombing of the Southeast Asian country proved far more catastrophic than anything we have witnessed thus far in Iraq.

Unlike the Iraq war, which was the creation of hawkish neo-conservatives, the architects of the Vietnam War were primarily Cold War liberals who believed they were at the forefront of a global crusade against communism. Since 1968, the Cold War has ended, only to be replaced by the post-9/11 war on terror. Yet the latter "war" lacks the breadth and focus of the former.

In fact, not surprisingly, today the war on terror is widely viewed as an American creation, with the debacle in Iraq being its most lethal manifestation.

Like 1968, America in 2008 faces a presidential campaign with an uncertain outcome. In 1968, antiwar "doves" and militaristic "hawks" battled for the soul of the Democratic party over the war in Southeast Asia.

Meantime, Richard Nixon -- a man who lost the presidential race to John F. Kennedy in 1960 and the California gubernatorial race two years later --made an astonishing comeback on the promise of "law and order" and a "secret plan" to end the war on Vietnam. The Nixon of 1968 appeared more confident and mature -- less of a rigid cold warrior -- than the Nixon of 1960. His appeal to the "silent majority" of "non-protesters" resonated with a traumatized public, especially at a time of so much unrest.

Flash forward to 2008. There is still polarization in America, but conservatives, not liberals, are setting the agenda. The failure of Vietnam contributed to the decline of liberalism in America, just as the failure of Iraq is undermining conservatives. Still, the current political landscape is characterized by a strong right and a weak left.

There are no Bobby Kennedys in the presidential race of 2008. The Republican contenders, simply put, don't share his humanistic world view.

Today's Democrats - with the exceptions of John Edwards and Dennis Kucinich - are too anchored down by their own poll-watching centrism to take the bold risks that Kennedy took four decades ago. Even Obama, for all the excitement he has generated, is not as daring or inspiring as Kennedy.

Despite the passage of 40 years, echoes of 1968 still reverberate. Much has changed. The Cold War is over, Vietnam has a flourishing market economy, and many countries once controlled by autocratic regimes are now freer places.

In the United States, though, the legacies of war, the assassinations of great visionaries, and the victory of Nixon's conservatism still shape the tenor of these times.

Andrew Hunt is chair of the department of history at the University of Waterloo.