The Black Death
Cities were hit hard by the plague. Financial business was disrupted as debtors died and their creditors found themselves without recourse. Not only had the debtor died, his whole family had died with him and many of his kinsmen. There was simply no one to collect from.
Construction projects stopped for a time or were abandoned altogether. Guilds lost their craftsmen and could not replace them. Mills and other special machinery might break and the one man in town who had the skill to repair it had died in the plague. We see towns advertising for specialists, offering high wages.
The labor shortage was very severe, especially in the short term, and consequently, wages rose. Because of the mortality, there was an oversupply of goods, and so prices dropped. Between the two trends, the standard of living rose . . . for those still living.
Effects in the countryside were just as severe. Farms and entire villages died out or were abandoned as the few survivors decided not to stay on. When Norwegian sailors finally visited Greenland again in the early 15thc, they found in the settlements there only wild cattle roaming through deserted villages.
Whole families died, with no heirs, their houses standing empty. The countryside, too, faced a short-term shortage of labor, and landlords stopped freeing their serfs. They tried to get more forced labor from them, as there were fewer peasants to be had. Peasants in many areas began to demand fairer treatment or lighter burdens.
Just as there were guild revolts in the cities in the later 1300s, so we find rebellions in the countrside. The Jacquerie in 1358, the Peasants' Revolt in England in 1381, the Catalonian Rebellion in 1395, and many revolts in Germany, all serve to show how seriously the mortality had disrupted economic and social relations.