Within the Bolshevik Party, Bukharin was initially a left communist, but gradually moved to the right from 1921. His strong support for and defence of the New Economic Policy (NEP) eventually saw him lead the Right Opposition. By late 1924, this stance had positioned Bukharin favourably as Joseph Stalin's chief ally, with Bukharin soon elaborating Stalin's new theory and policy of Socialism in One Country. Together, Bukharin and Stalin ousted Trotsky, Grigory Zinoviev and Lev Kamenev from the party at the 15th Communist Party Congress in December 1927. From 1926 to 1929, Bukharin enjoyed great power as General Secretary of the Comintern's executive committee. However, Stalin's decision to proceed with collectivisation drove the two men apart, and Bukharin was expelled from the Politburo in 1929.