The Masses was founded in New York in 1911 by Piet Vlag. Another important financial backer was Amos Pinchot, a wealthy lawyer who supported a wide variety of progressive causes.
Organised like a co-operative, artists and writers who contributed to the journal shared in its management. Vlag edited the socialist journal for a year but in 1912 appointed Max Eastman, a Marxist, to carry out this task.
Articles and poems were written by people such as John Reed, Sherwood Anderson, Crystal Eastman, Hubert Harrison, Inez Milholland, Mary Heaton Vorse, Louis Untermeyer, Randolf Bourne, Dorothy Day, Helen Keller, William Walling, Carl Sandburg, Upton Sinclair, Amy Lowell, Mabel Dodge, Floyd Dell and Louise Bryant.
The Masses also published the work of important artists including John Sloan, Robert Henri, Alice Beach Winter, Mary Ellen Sigsbee, Cornelia Barns, Reginald Marsh, Rockwell Kent, Art Young, Boardman Robinson, Robert Minor, K. R. Chamberlain, Stuart Davis, Cornelia Barns, George Bellows and Maurice Becker.
Max Eastman believed that the First World War had been caused by the imperialist competitive system. Eastman and journalists such as John Reed who reported the conflict for The Masses, argued that the USA should remain neutral. Most of those involved with the journal agreed with this view but there was a small minority, including William Walling and Upton Sinclair, who wanted the USA to join the Allies against the Central Powers. When Sinclair failed to convince his fellow members he resigned from the Socialist Party and ceased to contribute to The Masses.