In 1901, Filomeno Mata [es] appointed him a correspondent on Diario del Hogar and, that same year, he enlisted as a reservist in the National Army, where he reached the rank of second lieutenant (cavalry).

In 1905 he moved to San Francisco, California, where he published the newspaper Alba Roja ("Red Dawn"); In May 1906 Guerrero was visited by Manuel Sarabia, who invited him to participate on the Organizing Committee of the Mexican Liberal Party (JOPLM).

In addition to Alba Roja, Guerrero worked on other papers, including Revolución (1908) and Punto Rojo (1909), which had a weekly print-run of 10,000 copies in El Paso, Texas, and joined its voice to calls for a general strike;[2] he also contributed to Regeneración, published by the Flores Magón brothers.

Guerrero, who had been appointed Chief of Operations of the Confederation of Groups of the Liberal Army in Mexico, decided to raise an armed force in El Paso, Texas, and lead it across the border, even with the disapproval of the PLM's Organizing Committee, which wanted him to dedicate his efforts to writing and reporting.

[4] On 22 December, some 30 revolutionaries led by Guerrero entered Mexico through Ciudad Juárez, Chihuahua, attacked a hacienda, sequestered a train, and advanced toward the south, destroying the railway bridges as they passed.