Original sentence: In the zone known as the oprichnina, Ivan's followers carried out a series of bloody purges, culminating in the Massacre of Novgorod (1570).This so weakened Muscovy that the Crimean Tatars were able to sack Moscow and Ivan abandoned the oprichnina
Edited sentence: 1572 Ivan abandoned the oprichnina.In the zone known as the oprichnina, Ivan's followers carried out a series of bloody reprisals against the feudal aristocracy which he suspected of treachery after the betrayal of prince Kurbsky.The military losses, epidemics, poor harvests and the internal dissonance so weakened Muscovy that the Crimean Tatars (allies of Poland) were able to sack central Russian regions and burnt down Moscow