How successful was the League of Nations in the 1920s?

In the 1920s the League of Nations was mostly successful. The League successfully adjudicated the Aaland Islands dispute in 1921, preventing a military altercation between Sweden and Finland. Furthermore, the League resolved the issue of Upper Silesia in 1921, deciding to split the territory between both Germany and Poland, and bringing an end to the riots. However, these successes were relatively minor in comparison to its inherent structural flaws. For example, America, a leading military power, refused to join. This was problematic as American isolationism significantly detracted from the both the League's power and its legitimacy. Additionally, neither Germany nor Russia were initially allowed to join, resulting in the significant weakness of the League when dealing with larger countries. The League of Nations may have achieved minor successes in the 1920s, but this was at the cost of its future success, due to its inability to secure the support of important nations.