Simon Schama explores how American optimism about the infinite possibilities of its land and resources is in danger of coming to a grinding halt. Nowhere is this more evident than the American West, which has always been a symbol of opportunity and freedom. Oil at $4 a gallon may be dominating the headlines, but here it’s the lack of water that’s an even bigger threat to the American future. The West is in the grip of a nine-year drought.

America’s optimism about its natural resources has always been spiced with clashes over conservation, going back to the first man to navigate the Colorado River, John Wesley Powell. American ingenuity made farming on an industrial scale possible in the early years of the 20th century but at the cost of making Oklahoma a dustbowl. The building of the Hoover Dam, a modern American miracle, which provided essential irrigation for farming and for the new city of Las Vegas, now no longer supplies enough water for both.

In 1980, Ronald Reagan’s optimism about American plenty defeated Jimmy Carter’s campaign for self-restraint but, in this coming election, neither candidate can ignore the challenges facing America as it enters an era of limits.