"What is most striking about [Rome's] history is the speed of the Roman Empire's collapse. In just five decades, the population of Rome itself fell by three-quarters. Archaeological evidence from the late fifth century - inferior housing, more primitive pottery, fewer coins, smaller cattle - hows that the benign influence of Rome diminished rapidly in the rest of western Europe. What [Oxford historian Brian] Ward-Perkins calls 'the end of civilization' came within the span of a single generation.
"Other great empires have suffered comparably swift collapses. The Ming dynasty in China began in 1368, when the warlord Zhu Yuanzhang renamed himself Emperor Hongwu, the word hongwu meaning 'vast military power.' For most of the next three centuries, Ming China was the world's most sophisticated civilization by almost any measure. Then, in the mid-seventeenth century, political factionalism, fiscal crisis, famine, and epidemic disease opened the door to rebellion within and incursions from without. In 1636, the Manchu leader Huang Taiji proclaimed the advent of the Qing dynasty. Just eight years later, Beijing, the magnificent Ming capital, fell to the rebel leader Li Zicheng, and the last Ming emperor hanged himself out of shame. The transition from Confucian equipoise to anarchy took little more than a decade.
"In much the same way, the Bourbon monarchy in France passed from triumph to terror with astonishing rapidity. French intervention on the side of the colonial rebels against British rule in North America in the 1770s seemed like a good idea at the time - a chance for revenge after Great Britain's victory in the Seven Years' War a decade earlier - but it served to tip French finances into a critical state. In May 1789, the summoning of the Estates-General, France's long-dormant representative assembly, unleashed a political chain reaction that led to a swift collapse of royal legitimacy in France. Only four years later, in January 1793, Louis XVI was decapitated by guillotine. ...
"The sun set on the British Empire almost as suddenly. In February 1945, Prime Minister Winston Churchill was at Yalta, dividing up the world with U.S. President Franklin Roosevelt and Soviet Premier Joseph Stalin. As World War II was ending, he was swept from office in the July 1945 general election. Within a decade, the United Kingdom had conceded independence to Bangladesh, Bhutan, Burma, Egypt, Eritrea, India, Iran, Israel, Jordan, Libya, Madagascar, Pakistan, and Sri Lanka. The Suez crisis in 1956 proved that the United Kingdom could not act in defiance of the United States in the Middle East, setting the seal on the end of empire. Although it took until the 1960s for independence to reach sub-Saharan Africa and the remnants of colonial rule east of the Suez, the United Kingdom's [centuries old] age of hegemony was effectively over less than a dozen years after its victories over Germany and Japan.
"The most recent and familiar example of precipitous decline is, of course, the collapse of the Soviet Union. With the benefit of hindsight, historians have traced all kinds of rot within the Soviet system back to the Brezhnev era and beyond. Perhaps, as the historian and political scientist Stephen Kotkin has argued, it was only the high oil prices of the 1970s that 'averted Armageddon.' But this did not seem to be the case at the time. In March 1985, when Mikhail Gorbachev became general secretary of the Soviet Communist Party, the CIA estimated the Soviet economy to be approximately 60 percent the size of the U.S. economy. This estimate is now known to have been wrong, but the Soviet nuclear arsenal was genuinely larger than the U.S. stockpile. And governments in what was then called the Third World, from Vietnam to Nicaragua, had been tilting in the Soviets' favor for most of the previous 20 years. Yet less than five years after Gorbachev took power, the Soviet imperium in central and Eastern Europe had fallen apart, followed by the Soviet Union itself in 1991. If ever an empire fell off a cliff - rather than gently declining - it was the one founded by Lenin."
Niall Ferguson, Complexity and Collapse, Foreign Affairs, March/April 2010, pp. 28-30