SEP first formed in 1964 as the American Committee for the Fourth International, created by expelled members of the Socialist Workers Party.

[3] In 1958, SWP adopted a policy of "regroupment": Pursuit of former members of Stalinist communist parties, who had been disillusioned by the Secret Speech.

RT developed links with the Socialist Labour League in Britain, led by Gerry Healy.

[3]: 866, 917–918, 924  [5] ACFI maintained connections with Gerry Healy and the (non-merged portions of the) ICFI, which they considered the legitimate Trotskyist movement.

[citation needed] Wohlforth argued that the split was due to their demand for discussion of the decision by the Sri Lankan Trotskyist Lanka Sama Samaja Party to participate in the national government.

[3]: 924  ACFI characterized this decision as "opportunism" that originated in the "centrist" position of the LSSP during the split between the ISFI and ICFI of 1953.

The Workers Revolutionary Party (WRP) in Britain argued that ICFI should support nationalist leaders like Saddam Hussein and Muammar Gadhafi.

[1] In its list of transitional demands, the SEP includes: Universal employment, universal healthcare, ending foreclosures and evictions, workplace democracy, high inheritance taxes, nationalization of large corporations, and replacement of the volunteer-based US military with "popular militias controlled by the working class and with elected officers".