May was the month in which the west was won. On orders from President Jefferson, the great American pioneers Meriwether Lewis and William Clark left St Louis on 14 May 1804, and followed the Missouri River across the Great Plains into the uncharted west. In doing so, they helped to define America both as a nation of hardy frontiersmen untroubled by the obstacles of nature and as a land of Romantics wedded to the wonder of the great outdoors.
Two centuries later, a very different president is attempting to define a very different America: more bellicose, purposeful and partisan. Rather than safeguarding the United States mapped out by Lewis and Clark, George W Bush has spent the past four years dismantling his nation's environmental heritage. He has allowed roads into virgin forests, gas exploration in national parks, and maintained the sacrosanct rights of drivers of sport utility vehicles (SUVs) to cheap petrol. In so doing, the self-styled cowboy from the barren ranches of Crawford, Texas, has aligned himself firmly with the frontier strain of American identity.
The natural environment has always been contested terrain in the story of the US. From the earliest western encounters, the New World was recorded as a place of extraordinary beauty. Christopher Columbus believed he had arrived on the "nipple" of the earth, which reached closer to heaven than the rest of the world. The moral virtue, the godliness of America, was reflected in its seductive coastlines and fertile plains. Such natural innocence contrasted favourably with the corrupt, spoilt world of what Donald Rumsfeld would later christen "old Europe".
However, the Puritans of the 17th century and revolutionaries of the 18th did not adopt such a reverential attitude. The settlers of Virginia were determined to tame the savage wilderness and cultivate the earth for the glory of God. Similarly, the radicals of Pennsylvania revered science above nature. If America was to break free of the Old World, then the republic's natural riches must be exploited in the name of progress. In the north, that signalled industry; in the south, a landscape of ordered plantation.
But as America attempted to create itself as a nation, the natural environment started to command more lofty sentiments. Against the strains of a Romanticism that championed human relationship with nature, the continent's woods, swamps, plains and mountains were imbued with a richness beyond their mineral wealth. In Europe, people might have venerated medieval cathedrals or the ruins of Rome, but in the New World they celebrated their wilderness as a font of patriotism. In these primeval settings could be found the key to the American character: the individualism, the egalitarianism, the creativity.
In 1864, at the height of the American civil war, Abraham Lincoln appealed to this ideal by making a symbolic attempt to unite his fractured nation. Deploying what remained of his presidential authority, he handed over the rugged wilderness of the Yosemite Valley to the state of California for use as a public park. Once regarded as a godless settlement of Indians worthy of clearance, the valley now testified to a new conception of nationhood. Lincoln's gesture was designed to suggest there existed an America beyond the present divisions, uniting north and south, and it could be found in the extraordinary natural environment.
But it was the artists and writers of the emergent nation who most fulsomely celebrated their physical heritage. The Hudson Valley painters successfully crafted a sublime image of America as a modern Eden. Today, in New York's Metropolitan Museum of Art, the grandeur of Thomas Cole's epic landscapes - the oxbow rivers, fecund valleys and plunging ravines - still offer a sense of the profundity and magnificence of America.
Meanwhile, from the swamps of Concord, Massachusetts, the philosopher-poet Henry David Thoreau conjoined the American tradition of nonconformity with the rugged space and brittle wilderness of the natural environment. Nature became the animating spirit behind the American character. His words were echoed in a series of lyrical essays on nature by 19th-century America's most beloved author, Ralph Waldo Emerson. He rhapsodised on how "the stems of pines, hemlocks, and oaks, almost gleam like iron on the excited eye", and reminded his readers that "here no history, or church, or state, is interpolated on the divine sky and the immortal year".
None of these flights of fancy made much sense to the impoverished immigrant communities marching west. Where Lewis and Clark led, in the frontier states of Colorado, Utah and Arizona, there was precious little idealism about the natural world. Instead, just as their Puritan predecessors had done, the gold-diggers, ranchers and railwaymen who followed regarded the environment less as a symbol of national identity and more as a resource to be mined and harvested.
All of which worried the power-brokers in Washington, DC, increasingly attuned to the political significance of the wilderness. Fearing what the trek west could do to the landscape, the federal government began to establish a series of national parks beginning with Yellowstone, Wyoming, in 1872. The process gathered pace with the arrival of the Scottish naturalist and conservationist John Muir in California. His influential lobby group the Sierra Club ensured the establishment of Yosemite as a national park and, following it, the Grand Canyon and Sequoia.
Their work was continued under the presidencies of Theodore and Franklin D Roosevelt who, by expanding the network of national parks and monuments, helped to define the great outdoors as a uniquely American attribute. Federal legislation enacted a series of environmental safeguards, while the balance of parkland moved from the west to the east and started to encompass old civil war sites - so much so that, during the 20th century, the very identity of America became predicated on its natural monuments: the Florida Everglades, the Northern Rockies, the California Redwoods, even Yogi Bear's Jellystone Park.
However, since his arrival in office, President Bush has rejected this vision of America and reverted to the old Puritan impulse for exploitation. The America of the frontier, of less government and more hard-boiled robber barons, has subsumed the legacy of Thoreau and Emerson. Taking a lead from Bush's toxic policies as governor of Texas, the administration has declared its ideological hostility to government control of land or the regulation of industry. Nature has once again become a resource to be mastered and mined.
The budget of the Environmental Protection Agency has been slashed (leading to the departure of one of the few moderate Republicans, Christine Todd Whitman), while its enforcement division has been persuaded to ease up on prosecutions. The highly successful Superfund programme for cleaning up toxic waste has been stripped of resources, reforms to the Clean Air Act and Clean Water Act have allowed corporations to pollute with impunity and federal protection has been removed from fragile environments, while energy lobbyists have been granted plum departmental jobs. The most grotesque example is J Steven Griles, former chief lobbyist for America's oil, gas and coal conglomerates, who is now deputy secretary of the Department of the Interior. As well as continuing to receive money from his former employers, Griles has worked tirelessly to undermine environmental controls while promoting the industrial interests of his old clients. Meanwhile, his colleague Mark Rey, a veteran timber lobbyist and now under-secretary for agriculture, is helping out his old friends by allowing three million acres of land to be put up for timber sales in Alaska's Tongass National Forest.
The result has been millions of acres of wilderness opened up to logging, mining, oil and gas drilling. Under the so-called Healthy Forests Initiative, the timber industry has been allowed to attack the old-growth trees of the Californian national parks; in the name of energy security, wells are being sunk in the wilds of Montana and Wyoming; and under the guise of less government, the interior secretary, Gale Norton, has gutted Clinton-era protection for road-free national parks. In Florida, the miraculous ecosystem of the Everglades is being destroyed by new rules allowing suburban development and army engineering. The Grand Canyon National Park has been opened up for development. And all the while, Alaska awaits the next attempt to ruin its pristine wilderness in the search for cheap oil.
Bush's environmental programme is a wholesale assault on the Romantic traditions of American national identity. The natural calm of the US wilderness has been replaced by a different history of revolutionary, Puritanical zeal. President Bush is building his re-election campaign around defending a nation at war, but in truth, the American homeland has never looked more in danger.