Branches also took part in activism against the Iraq War, against police brutality, against the death penalty, and in labor strikes and other social movements.

[4] The ISO experienced discord in early 2019, upon exposure that its leadership mishandled an accusation of sexual assault in 2013 and voted to dissolve itself shortly afterward.

The organization believed that this working-class majority could end capitalism by leveraging their power over production through mass strikes.

[7] The organization tended to follow Cliff's view of these governments as state capitalist, although not all members held this analysis.

For this reason, the organization saw itself as a preliminary group that could help to win reforms and raise consciousness until such time that a revolutionary party could be formed.

In the final years of its existence, the organization was more strongly aligned with socialist feminist ideas and particularly Black feminism and intersectionality.

The ISO originated in 1976 among groups in the American International Socialists (IS) that were growing increasingly critical of the organization's leadership.

The Left Faction and its international supporters maintained that the IS's leadership had acquired a top-down style of operating that depoliticized the organization and placed too much emphasis on sending student activists into working class employment (a tactic referred to as "industrialization").

[14] The ISO began publication of its paper, Socialist Worker, shortly after its formation and produced a monthly print version and, later, a daily updated website until 2019.

Juan Cruz Ferre writes, "The ISO famously managed to thrive during the worst years of neoliberalism and working-class retreat.

[22] By 2009, members argued that it was "by far the largest socialist organisation in the United States today, attracting to revolutionary ideas a much larger number of young activists than any of the others.

[23][24] Even after the split with the IST, ISO continued to receive informal guidance from leaders of the UK SWP, such as Chris Harman.

The ISO sharply rebuked Alex Callinicos for his "bureaucratic tendencies" in maintaining control in the fallout of a rape allegation.

It was soon revealed that the leadership at the time forced the national appeals committee of the ISO to overturn an earlier finding of rape in order to clear the accused.

[1] The ISO published a daily online and monthly print newspaper, Socialist Worker, with a bi-monthly Spanish language supplement, Obrero Socialista.

[40] The ISO also distributed the International Socialist Review and titles from the publishing house Haymarket Books, both of which were run by the non-profit Center for Economic Research and Social Change.

[48] In California in 2006, ISO member Todd Chretien ran against Dianne Feinstein for the Senate seat on the Green Party ticket, receiving 139,425 votes (1.8 percent).

[49] In 2013, the ISO endorsed Socialist Alternative's Kshama Sawant in her successful Seattle City Council election.

[51] Speakers at past Socialism conferences include filmmaker and author Tariq Ali, actors Wallace Shawn and John Cusack, The Nation writers Jeremy Scahill and Dave Zirin, journalists Amy Goodman, Glenn Greenwald, scholar Keeanga-Yamahtta Taylor, environmental writer John Bellamy Foster, science-fiction author China Miéville, Iraq Veterans Against the War member Camilo Mejía, Palestinian rights activists Omar Barghouti and Ali Abunimah.