Study history long enough and it begins to implode, as if all the disparate fragments of the past want to condense into patterns that illuminate the present. This is precisely the effect created by the twice Pulitzer Prize winning author and respected historian, Barbara W. Tuchman.

In one of the most esteemed of her many books, A Distant Mirror: The Calamitous 14th Century, she describes a time of great castles, fantastic crusades and soaring cathedrals set amid a social climate of political ferocity, spiritual turmoil and the horrific ravages of the Black Death. Those ten decades nearly ruined Europe. But the tumult and destruction was also a cleansing and a revitalizing that eventually culminated in the modern world.

Now, as the calamitous 20th century transitions into the early years of the 21st century, the time again invites us to review our history. And again, another of Tuchman's books has much to teach us. Although the March of Folly: From Troy to Vietnam was written in 1984, its perspective is uncomfortably current and poignantly relevant given the critical environmental issues facing us today.

The substance of this book is the appalling litany of failures in judgment by political leaders over the 2,500 years from the war between the ancient Greeks and Trojans to the disaster of America in Vietnam. And if history and human nature are consistent, then we might expect the same failures of judgment to apply to the present.

Tuchman didn't live long enough to write about the Bush Administration's grave misjudgment in Iraq or the multi-fronted environmental crisis facing us today. But she was clear about four earlier events. The Trojans knew the horse was a ruse. The Renaissance popes knew they were provoking the "protestants" to open secession. The British knew their heavy hand in North America would incite the Americans to rebellion. The US knew Vietnam was a losing cause. But, as Tuchman so poignantly concluded, "The power to command frequently causes failure to think."

Unfortunately, history is replete with other tragic failures. The nations of 1914 stumbled into World War I with a known litany of stupid and arrogant mistakes. Then the victors of the Great War —" the war to end all wars" — imposed the reparation conditions that would inevitably generate a hostile response from Germany. The blood and dust of World War II had barely settled when the Cold War began and civilization came within a hair's breadth of nuclear annihilation.

How close? John Ibbitson, writing in The Globe & Mail of July 30/08, cites a chilling instance during the Cuban missile crisis. In October, 1962, as an American blockade of arms shipments to Cuba was under way, US warships were trying to force a Soviet submarine to the surface with depth charges. The submarine's captain decided to launch a nuclear-tipped torpedo at the American warships, an event that would likely have precipitated a nuclear exchange between America and the Soviets. Only impassioned pleas from the Soviet sub's crew dissuaded the captain from launching the torpedo. Sometimes the whole course of human history balances on such moments.

The multitude of environmental problems we face today have possible consequences that are comparable to a nuclear holocaust. The numerous causes and the likely effects are now fairly clear to us. We have known for almost 200 years about the dangers of a burgeoning human population. For 50 years we have been "strip mining" the world's oceans of fish, with reasonable certainty what the sorry result will be. Concerned people in the 1960s were warning of "environmental collapse" — the specific mechanisms were unclear but the general principle was an unstoppable unravelling of damaged ecosystems. During the early 1970s we identified the fragility and brevity of our "petro-civilization" but we are still addicted to oil. It's now been 20 years since the dynamics of global warming have been clearly described and documented.

All this knowledge has done little to change our behaviour. Population is skyrocketing. We still haven't curtailed industrial fishing or placed a third of the world's oceans in marine reserves to help rebuild depleted fish stocks. Global ecosystem damage is increasing, not decreasing. World oil consumption continues to rise — demand is expected to be 104 million barrels per day by 2020 but supply will likely peak at 100 million barrels per day by 2012. Token efforts to reduce carbon dioxide emissions have allowed the rates are going up faster than at any time in history.

Should the whole or even a part of this unfolding environmental crisis comes to pass, it will make our litany of past follies seem comparatively trivial.

If we return to Tuchman's first example of human folly, we must hope that only the Trojan leaders knew the horse was a ruse. Perhaps the lack of communication 2,500 years ago meant that the Trojans themselves were ignorant of the horse's deadly content.

But in today's world, a people who are emersed in a sea of print and electric information no longer have the excuse of ignorance. Indeed, we know we have several deadly horses within our gates, we know that indifference and inaction are no longer options, and we know we must direct our leaders to act for our well-being.

Surely our history has enough failures of judgment without us adding more. Unless, of course, as Barbara Tuchman ominously reminds us, "Character is fate."