On January 29, 1911, a coalition of Mexican revolutionaries and members of the Industrial Workers of the World (IWW), a US-based anti-capitalist labor union, crossed the border between California and the Mexican state of Baja California to launch what would come to be known as the Baja Insurrection. Many of the Mexicans belonged to the Partido Liberal Mexicano (PLM), which had announced its intentions of toppling Mexican dictator Porfirio Díaz, transferring the ownership of factories to their workers, and returning lands to Indigenous communities. Driven from Mexico to the United States by Díaz, the PLM had found solidarity with the IWW, which similarly advocated for workers’ control of production.

Growing from a small band of less than two dozen revolutionaries to hundreds of PLM members, their supporters (including Indigenous tribespeople), and IWW members, the insurrectionists seized the towns of Mexicali, Algodones, Tecate, and Tijuana, opening an early northwestern front in the Mexican Revolution. The insurrectionaries were supported by arms and funds from US radicals, including the Socialist Party — which, combined with the prospect of thousands of US-based Mexicans joining the revolution, pushed president William Taft to act.

Twenty thousand US troops sealed the border, while the US Navy secured access to ports in Baja California for Díaz’s forces. The insurrectionists held out for six months, but, without any means of reinforcing or resupplying themselves, ultimately quit the campaign. Some of them subsequently flocked to the banner of Francisco Madero, a centrist, US-backed opponent of Díaz, but those who had crossed the border were summarily arrested by US authorities for violating neutrality laws.