The United Opposition (sometimes also called the Joint Opposition) was a group formed in the All-Union Communist Party (Bolsheviks) in early 1926, when the Left Opposition led by Leon Trotsky, merged with the New Opposition led by Grigory Zinoviev and his close ally Lev Kamenev, in order to strengthen opposition against the Joseph Stalin led Centre. The United Opposition demanded, among other things, greater freedom of expression within the Communist Party and less bureaucracy.
The grouping was proposed by the Group of 15, a small faction around Vladimir Smirnov which claimed that the Soviet Union was no longer a workers' state. They brought together Trotsky's Left Opposition and Zinoviev's New Opposition (also known as the Opposition of 1925), despite them both having many differences with the Group of 15, particularly over the question of whether the Soviet Union was still a workers' state. Many former supporters of the Workers Opposition also joined the United Opposition.
Smirnov's Group of 15 left the United Opposition soon after, over increasing differences between themselves and Kamenev and Zinoviev's supporters. In October 1926, Stalin's supporters voted Trotsky out of the Politburo. Many supporters of Kamenev and Zinoviev's group, as well as most from the Workers Opposition grouping, had left the United Opposition by mid-1927, changing sides under the growing political pressure and espousing their support for Stalin.
In November 1927, the United Opposition held a demonstration in Red Square, Moscow, along with Vladimir Lenin's widow, Nadezhda Krupskaya. However, the United Opposition were unable to gain the support of more than a small minority of the Communist Party, and were expelled in December 1927 after the Congress declared United Opposition views to be incompatible with Communist Party membership. Trotsky formed the International Left Opposition with his remaining supporters, and the Group of 15 also continued its opposition to Stalin. Supporters of these groups were soon exiled or imprisoned, and by the end of 1941, nearly all former supporters of the United Opposition, whether or not they had repudiated it, had been executed or assassinated on Stalin's orders.
Despite various attempts at a rapprochement, the International Left Opposition and the Group of 15 were unable to agree on a further platform after 1927.