Original sentence: After the sacking of 1237-1238, when the Mongols burned the city to the ground and killed its inhabitants, Moscow recovered and became the capital of an independent principality.The defenses were hardly successful, as in 1177 the city was burned to the ground and its population was killed
Edited sentence: After the sacking of 1237-1238, when the Mongols burned the city to the ground and murdered its inhabitants, Moscow recovered and became the capital of an independent principality.The defenses were hardly successful, as in 1177 the city was burned to the ground and its population was murdered