 While Lenin had been ill Stalin had forged an anti-Trotsky alliance with Kamenev and Zinoviev.Although Zinoviev was concerned about Stalin's growing authority, he rallied behind him at the 13th Congress as a counterweight to Trotsky, who now led a party faction known as the Left Opposition.The Left Opposition believed the NEP conceded too much to capitalism; Stalin was called a "rightist" for his support of the policy.