The main reasons why the League of Nations failed overall:

French and British self interest wouldn't abandon these to support league.
Absent powers include USA and Russia. Lacked authority and sanctions inefficient.
Inefficient sanctions. Sanctions were meant to be the League's biggest weapon but without USA they didn't work. Broken easily
Lack of armed forces. The League of Nations had no armed forces of its own. Britain and France never fought for the league
Unfair treaties. Too harsh so the league had trouble imposing them
Reached decisions too slowly. Sanctions didn't work because they
were too slow. Met too infrequently.