Revolutions are rare. Most unhappy societies, most of the time, do not rise up, and most uprisings fail. So the question is not only why people are angry but why anger sometimes turns into a collapse of the state. Scholars have offered several families of answers, each catching something real.

Discontent and expectations

In 1962 the political scientist James C. Davies proposed what became known as the J-curve. Revolutions, he argued, are most likely when rising expectations meet a sudden reversal: a long stretch of improving conditions is followed by a short, sharp downturn. People who have grown used to progress judge the present against what they had come to expect, and the gap feels intolerable. In 1970 Ted Robert Gurr built a wider theory around relative deprivation, defined as a gap between what people expect and what they get. On this view, hunger alone does not cause revolt; the sense of being cheated does.

These ideas explain why revolutions often come in periods of growth rather than in the depths of misery. Their weakness is the mirror image. Discontent is common but revolutions are rare, so a theory built on grievance predicts far more uprisings than ever happen. Grievance is also hard to measure before the event and easy to find after it.

Organization and opportunity

Charles Tilly and others answered that angry people need more than anger. They need organizations, leaders, money, ways to communicate and a moment when the authorities look weak or divided. A strong, united state can absorb enormous resentment for decades. A divided one can fall to a modest push. Tilly also stressed that governments and challengers learn from each other over time, so protest tactics and policing change together. This shifted attention from the feelings of the crowd to the balance of resources between rulers and challengers.

When states break

Theda Skocpol went further and set the crowd's intentions almost aside. Studying France, Russia and China, she argued that social revolutions begin in state breakdown under outside pressure. Costly wars and competition with stronger rivals drained treasuries, split rulers from landed elites and paralyzed armies; only then could peasant revolts spread and new groups seize power. She borrowed a line from the American abolitionist Wendell Phillips, who said in 1852: "Revolutions are not made; they come." In other words, revolutions come rather than being made by plotters. Critics replied that this underrates ideas, leaders and religion. Iran in 1979, where a cleric's message mobilized millions against a state with a large, well-funded army, pushed Skocpol herself to give culture more weight.

Population and pressure

Jack Goldstone, studying England in the 1640s, France in 1789, the fall of China's Ming dynasty and crises in the Ottoman Empire, offered a demographic-structural theory. Its core is population growth straining states and elites. When populations grow faster than the economy, prices rise and real wages fall; governments find their taxes buy less; more young men from elite families compete for a fixed number of offices and estates. A fiscal crisis at the top, bitter rivalry among elites and misery below combine into a revolutionary mix. The theory joins structure and grievance, though it fits agrarian empires better than modern cities.

Hidden opinion and sudden cascades

None of these theories explains why revolutions so often surprise everyone, including the secret police. The economist Timur Kuran offered an answer in 1991. Under repression, people practice preference falsification: people hiding their real views under pressure, praising a regime in public while loathing it in private. Because everyone hides, no one knows how many others feel the same. Each person has a personal threshold: some will protest if a hundred others do, some only if a hundred thousand do. When a few brave people act, others with low thresholds join, which brings in those with higher ones, and a cascade can sweep through a society in days. This is why the collapse looks inevitable afterward but invisible beforehand: hidden opposition can surface all at once.

Worked example: East Germany, autumn 1989

East Germany in 1989 lets us test each lens. The grievance lens finds plenty of material: shortages, stagnating living standards and nightly West German television showing what life could be. Yet those conditions had existed for years. The opportunity lens points to the summer, when Hungary opened its border with Austria and tens of thousands of East Germans fled through it, and to signals from Moscow that Soviet troops would not save the regime. The state's ability to use force was suddenly in doubt.

Kuran's lens explains the speed. In Leipzig, small prayer meetings at the Nikolai Church had been followed by Monday marches. On 9 October about 70,000 people marched while armed units waited, and no order to shoot came. Once that night showed that marching was survivable, people who had hidden their views for decades joined in, and the crowds in Leipzig and other cities grew week by week. Within a month the border was open and the ruling party was disintegrating. No single theory tells the whole story, but together they show grievance, a cracking state and a cascade of revealed opinion working at once.