What event served to significantly destabilize Ivan IV, contributing to his reputation as "the Terrible"? betrayal by his brother the sudden death of his wife invasion by Baltic crusaders

The sudden death of Ivan IV's beloved wife, Anastasia Romanovna, in 1560 had a profound impact on him. Her passing plunged Ivan into a deep sorrow that he never truly recovered from, leading him to paranoia and erratic behavior. This emotional turmoil was a turning point, marking a shift in his reign from relatively stable governance to oppressive measures and violent reprisals against perceived enemies, cementing his reputation as "the Terrible." As Ivan's grief intensified, he began to suspect those around him of treachery, leading to a series of brutal purges. This time was marked by the creation of the Oprichnina, a special regime that targeted the nobility and dissenters, further fueling his legacy of tyranny. This downward spiral set the stage for future instability in Russia long after his reign.