Short Answer 
Stalin sought absolute authority to unite the USSR and promote socialism. He defeated political rivals like Leon Trotsky to solidify his power and implemented violent repression to maintain control, ultimately transforming the USSR into a major global force.
Step 1: Establishing Absolute Authority
Joseph Stalin believed that he required absolute authority in the USSR to effectively unite and strengthen the nation. He aimed to build a coherent ideology that would promote the advancement of socialism across a united country. This belief was crucial for his political maneuvering, as it set the stage for his eventual takeover.
Step 2: Defeating Political Rivals
To solidify his control, Stalin engaged in a power struggle, notably defeating Leon Trotsky. His victory over Trotsky was not merely political but also ideological, as he positioned himself as the true advocate for Communism in Russia. This conflict underscored his resolve to eliminate opposition and to consolidate his grip on power.
Step 3: Implementing Repressive Tactics
Once in absolute power, Stalin resorted to violent tactics and widespread repression to maintain control. These methods included purges, forced labor camps, and state-sponsored terror. Although brutal, these actions were instrumental in transforming the USSR into a formidable global economic and military power, ultimately ensuring his legacy as a leader.