Final answer:
Ivan IV created the Oprichnina to combat the powerful boyars and strengthen his autocratic rule by establishing a separate territory under his direct control, which led to purges of the nobility.
Step-by-step explanation:
The best explanation for why Ivan IV created the Oprichnina during his reign is that Ivan IV was struggling against the boyars and wanted to limit their power. This was part of his efforts to consolidate autocratic control over the Russian state. The Oprichnina was a policy established by Ivan IV, also known as Ivan the Terrible, which involved creating a separate territory within Russia that was directly controlled by the tsar and protected by a loyal force known as the Oprichniki.
The creation of this territory allowed Ivan IV to carry out large-scale purges of the nobility, including the boyars, who were seen as a threat to his power. The Oprichnina was a tool to break the power of the nobility and strengthen the central authority of the tsar, illustrating the ongoing tension between centralized power and the interests of the landed aristocracy in Russia.