Los Angeles - NEW Year's weekend traditionally is a time for us to reflect, and to make resolutions based on our reflections. In this fresh year, with the United States seemingly at the height of its power and at the start of a new presidential term, Americans are increasingly concerned and divided about where we are going. How long can America remain ascendant? Where will we stand 10 years from now, or even next year?  Such questions seem especially appropriate this year. History warns us that when once-powerful societies collapse, they tend to do so quickly and unexpectedly. That shouldn't come as much of a surprise: peak power usually means peak population, peak needs, and hence peak vulnerability. What can be learned from history that could help us avoid joining the ranks of those who declined swiftly? We must expect the answers to be complex, because historical reality is complex: while some societies did indeed collapse spectacularly, others have managed to thrive for thousands of years without major reversal.  When it comes to historical collapses, five groups of interacting factors have been especially important: the damage that people have inflicted on their environment; climate change; enemies; changes in friendly trading partners; and the society's political, economic and social responses to these shifts. That's not to say that all five causes play a role in every case. Instead, think of this as a useful checklist of factors that should be examined, but whose relative importance varies from case to case.  For instance, in the collapse of the Polynesian society on Easter Island three centuries ago, environmental problems were dominant, and climate change, enemies and trade were insignificant; however, the latter three factors played big roles in the disappearance of the medieval Norse colonies on Greenland. Let's consider two examples of declines stemming from different mixes of causes: the falls of classic Maya civilization and of Polynesian settlements on the Pitcairn Islands.  Maya Native Americans of the Yucatan Peninsula and adjacent parts of Central America developed the New World's most advanced civilization before Columbus. They were innovators in writing, astronomy, architecture and art. From local origins around 2,500 years ago, Maya societies rose especially after the year A.D. 250, reaching peaks of population and sophistication in the late 8th century.  Thereafter, societies in the most densely populated areas of the southern Yucatan underwent a steep political and cultural collapse: between 760 and 910, kings were overthrown, large areas were abandoned, and at least 90 percent of the population disappeared, leaving cities to become overgrown by jungle. The last known date recorded on a Maya monument by their so-called Long Count calendar corresponds to the year 909. What happened?  A major factor was environmental degradation by people: deforestation, soil erosion and water management problems, all of which resulted in less food. Those problems were exacerbated by droughts, which may have been partly caused by humans themselves through deforestation. Chronic warfare made matters worse, as more and more people fought over less and less land and resources.  Why weren't these problems obvious to the Maya kings, who could surely see their forests vanishing and their hills becoming eroded? Part of the reason was that the kings were able to insulate themselves from problems afflicting the rest of society. By extracting wealth from commoners, they could remain well fed while everyone else was slowly starving.  What's more, the kings were preoccupied with their own power struggles. They had to concentrate on fighting one another and keeping up their images through ostentatious displays of wealth. By insulating themselves in the short run from the problems of society, the elite merely bought themselves the privilege of being among the last to starve.  Whereas Maya societies were undone by problems of their own making, Polynesian societies on Pitcairn and Henderson Islands in the tropical Pacific Ocean were undone largely by other people's mistakes. Pitcairn, the uninhabited island settled in 1790 by the H.M.S. Bounty mutineers, had actually been populated by Polynesians 800 years earlier. That society, which left behind temple platforms, stone and shell tools and huge garbage piles of fish and bird and turtle bones as evidence of its existence, survived for several centuries and then vanished. Why?  In many respects, Pitcairn and Henderson are tropical paradises, rich in some food sources and essential raw materials. Pitcairn is home to Southeast Polynesia's largest quarry of stone suited for making adzes, while Henderson has the region's largest breeding seabird colony and its only nesting beach for sea turtles. Yet the islanders depended on imports from Mangareva Island, hundreds of miles away, for canoes, crops, livestock and oyster shells for making tools.  Unfortunately for the inhabitants of Pitcairn and Henderson, their Mangarevan trading partner collapsed for reasons similar to those underlying the Maya decline: deforestation, erosion and warfare. Deprived of essential imports in a Polynesian equivalent of the 1973 oil crisis, the Pitcairn and Henderson societies declined until everybody had died or fled.  The Maya and the Henderson and Pitcairn Islanders are not alone, of course. Over the centuries, many other societies have declined, collapsed or died out. Famous victims include the Anasazi in the American Southwest, who abandoned their cities in the 12th century because of environmental problems and climate change, and the Greenland Norse, who disappeared in the 15th century because of all five interacting factors on the checklist. There were also the ancient Fertile Crescent societies, the Khmer at Angkor Wat, the Moche society of Peru -- the list goes on.  But before we let ourselves get depressed, we should also remember that there is another long list of cultures that have managed to prosper for lengthy periods of time. Societies in Japan, Tonga, Tikopia, the New Guinea Highlands and Central and Northwest Europe, for example, have all found ways to sustain themselves. What separates the lost cultures from those that survived? Why did the Maya fail and the shogun succeed?  Half of the answer involves environmental differences: geography deals worse cards to some societies than to others. Many of the societies that collapsed had the misfortune to occupy dry, cold or otherwise fragile environments, while many of the long-term survivors enjoyed more robust and fertile surroundings. But it's not the case that a congenial environment guarantees success: some societies (like the Maya) managed to ruin lush environments, while other societies -- like the Incas, the Inuit, Icelanders and desert Australian Aborigines -- have managed to carry on in some of the earth's most daunting environments.  The other half of the answer involves differences in a society's responses to problems. Ninth-century New Guinea Highland villagers, 16th-century German landowners, and the Tokugawa shoguns of 17th-century Japan all recognized the deforestation spreading around them and solved the problem, either by developing scientific reforestation (Japan and Germany) or by transplanting tree seedlings (New Guinea). Conversely, the Maya, Mangarevans and Easter Islanders failed to address their forestry problems and so collapsed.  Consider Japan. In the 1600's, the country faced its own crisis of deforestation, paradoxically brought on by the peace and prosperity following the Tokugawa shoguns' military triumph that ended 150 years of civil war. The subsequent explosion of Japan's population and economy set off rampant logging for construction of palaces and cities, and for fuel and fertilizer.  The shoguns responded with both negative and positive measures. They reduced wood consumption by turning to light-timbered construction, to fuel-efficient stoves and heaters, and to coal as a source of energy. At the same time, they increased wood production by developing and carefully managing plantation forests. Both the shoguns and the Japanese peasants took a long-term view: the former expected to pass on their power to their children, and the latter expected to pass on their land. In addition, Japan's isolation at the time made it obvious that the country would have to depend on its own resources and couldn't meet its needs by pillaging other countries. Today, despite having the highest human population density of any large developed country, Japan is more than 70 percent forested.
THE ENDS OF THE WORLD AS WE KNOW THEM**Jared Diamond Op-Ed article contends that several once powerful societies like Mayan and Polynesian collapsed because they did not take their environmental problems seriously; holds that US, to save itself, does not need new technology, it just needs political will to face up to its problems of population and environment; drawing (M)