DeLeon was of South American ancestry, who early immigrated to New York.  For a time he was teacher of languages at Columbia College; later he devoted himself thoroughly to socialist propaganda.  He established his first connection with the labor movement in the George campaign in 1886 and by 1890 we find him in control of the socialist organization.  DeLeon was impatient with the policy of slow permeation carried on by the socialists.  A convinced if not fanatical Marxian, his philosophy taught him that the American labor movement, like all national labor movements, had, in the nature of things, to be socialist.  He formed the plan of a supreme and last effort to carry socialism into the hosts of the Knights and the Federation, failing which, other and more drastic means would be used.

By 1895 he learned that he was beaten in both organizations; not, however, without temporarily upsetting the groups in control.  For, the only time when Samuel Gompers was defeated for President of the Federation was in 1894, when the socialists, angered by his part in the rejection of the socialist program at the convention,[77] joined with his enemies and voted another man into office.  Gompers was reelected the next year and the Federation seemed definitely shut to socialism.  DeLeon was now ready to go to the limit with the Federation.  If the established unions refused to assume the part of the gravediggers of capitalism, designed for them, as he believed, by the very logic of history, so much the worse for the established trade unions.

Out of this grew the Socialist Trade and Labor Alliance as a life and death rival to the Federation.  From the standpoint of socialism no more unfortunate step could have been taken.  It immediately stamped the socialists as wilful destroyers of the unity of labor.  To the trade unionists, yet fresh from the ordeal of the struggle against the Knights of Labor, the action of the socialists was an unforgivable crime.  All the bitterness which has characterized the fight between socialist and anti-socialist in the Federation verily goes back to this gross miscalculation by DeLeon of the psychology of the trade union movement.  DeLeon, on his part, attributed the action of the Federation to a hopelessly corrupt leadership and, since he failed to unseat it by working from within, he now felt justified in striking at the entire structure.

The Socialist Trade and Labor Alliance was a failure from the outset.  Only a small portion of even the socialist-minded trade unionists were willing to join in the venture.  Many trade union leaders who had been allied with the socialists now openly sided with Gompers.  In brief, the socialist “revolution” in the American labor world suffered the fate of all unsuccessful revolutions:  it alienated the moderate sympathizers and forced the victorious majority into taking up a more uncompromising position than heretofore.