Historical development of 12-note music

The technique of alteration in Liszt, Wagner, Mahler, Strauss, Reger, Pfitzner, etc. led to a loss of tonal relationship which ended in atonality. The means of expression with the previous material seemed to have been exhausted. Intermediate stages with bi- and poly-tonality had already occurred, 12-note passages appeared in various compositions. The Russian composer Jef Golyscheff (1897-1970) used a 12-note row in a string quartet as early as 1914. The mystical importance of the number 12 was not without importance in this development.
Schönberg tried to combine these theoretical attempts into a new and teachable order. As his solution he produced the "method of composition with 12 notes only related to each other."

What was Schönberg's merit for twelve-note music?