SWP is a shoot off the Socialist Party:
When the development of the WP was cut short by the rapid growth of the Socialist Party, George Breitman recalls that Shachtman and Cannon successfully proposed that the U.S. Workers Party, should dissolve, so that its members could recruit to Trotskyism from inside the Socialist Party.
At the SWP's founding congress, Burnham proposed that the USSR was no longer a degenerated workers' state: Shachtman spoke for the majority view that it remained a workers' state, and considered it important enough to hold a vote by roll call on the resolution
In 1938, Shachtman shocked Trotsky by publishing an article in the New International in which James Burnham declared his opposition to dialectical materialism, the philosophy of Marxism. Although Trotsky reassured Shachtman, "I did not deny in the least the usefulness of the article you and Burnham wrote," the issue would soon be revived as Shachtman and Trotsky clashed on the outbreak of World War II.
Following the Molotov-Ribbentrop Pact (August 23, 1939, a non-aggression treaty between Nazi Germany and the Soviet Union), the combined Invasion of Poland (September 1 - October 6, 1939) resulted in German and Soviet occupation of Poland. Inside the SWP, Shachtman and James Burnham argued in response that the SWP should drop its traditional position of unconditional defense of the USSR in war. The differences intensified with the outbreak of the Winter War (November 30, 1939 - March 12, 1940), when the Soviet Union invaded Finland. Shachtman and his allies broke with Cannon and the majority of the SWP leadership, which along with Trotsky continued to uphold unconditional critical defense of the USSR.
Trotsky was especially critical of Shachtman's role as a member of the International Executive Committee of the Fourth International. At the start of World War II, the Fourth International was placed under the control of a resident committee formed by IEC members who happened to be in New York City. Shachtman's tendency held a majority of the resident IEC. Trotsky and others criticized Shachtman for failing to convene the resident IEC or using its authority to reduce the tensions developing in the SWP.
a special convention was held in April 1940. After the April 1940 convention of the SWP, when Shachtman and his supporters on the new Political Committee refused to a vote on a motion pledging each member to abide by the convention decisions, they were expelled from the party. The minority excluded from the SWP represented 40% of its membership and a majority of the youth group
While Cannon and his allies regarded the Soviet Union as a "degenerated workers' state", Shachtman and his party argued that the Stalinist bureaucracy was following an imperialist policy in Eastern Europe. After a four-sided debate in 1940-41 in the new Workers Party between advocates of different theories, a majority concluded that the bureaucracy had become a new ruling class in a society they called "bureaucratic collectivist."
In the early 1940s, Shachtman further developed the idea, already used by Trotskyists in the 1930s, of a "Third Camp", an independent revolutionary force, made up of the world working class, movements resisting fascism and colonial peoples in rebellion, that would side neither with the Axis nor the Allies. – interesting.