The Fall of the Han Dynasty
Corruption, court intrigue, and famine drove desperate peasants into the Yellow Turban Rebellion, a massive uprising that broke the Han dynasty's grip and plunged China into generations of warlord chaos. War and disease then swept the land, and the recorded population fell catastrophically. Remarkably, it struck at almost exactly the same time as Rome's own third-century near-collapse — two great empires at opposite ends of the Silk Road convulsing in parallel, hinting at shocks that spanned the whole connected world.
Hardship plus a sudden opening (weak state, lost war, fiscal collapse) lets those who bear it overthrow the order — usually installing a new elite.