Serfdom, the Black Death and the 100 Years’ War set the austere preconditions for the Peasants’ Revolt in 1381, ultimately triggered by a random tax collector. The revolt was suppressed but fear of another rebellion led to a small reform in the royal council, a decrease in war expenditure and more careful management of local political power. Revolt and reform represent two possible results of the pressure of resistance, explode or vent respectively. A reform is in this sense a compromise between revolutionary and reactionary forces designed to temporarily calm things down to maintain the status quo. The pattern can be described as suffering -> trigger -> revolt -> reaction -> reform -> repeated suffering. Each of these steps may involve a complex of different phenomena and each step may be repeated more than once before advancing.
I’m going to focus on Europe here, but I’ll skip a lot of details, including the entire Reformation although it follows the same pattern. In 18th century France the conditions were nobility, war, austerity -> leading to the reform of a general assembly -> back to the same preconditions -> triggered by the dismissal of the finance minister -> the Storming of the Bastille -> Louis XVI failed to react -> reform for male suffrage and abolition of feudalism -> Prussia, Austria, Britain and others declared war on the French Republic -> Napoleon reconstructed France as an empire and conquered much of Europe -> nationalism fought back -> Communist Manifesto -> Bismarck countered the workers’ movement by uniting the German nation through war and reintroducing the reform of male suffrage -> Serb revolutionary killed heir to the Austro-Hungarian Empire triggering WW1 -> WW2 -> Cold War -> Today we have hundreds of armed conflicts caused by centuries of oppression of varying and intersecting character, dozens of resistance movements (including Black Power, Gay Pride, Feminism, Animal Liberation, Anonymous, indigenous’ rights, anti-colonialism et cetera) and consequently a long array of reforms.