The League was too much corrupt, and it thought for the interests of individuals and not collectively. E.g. collective security(military sanctions)

In the League, decisions could only be made if the vote was unanimous, and countries in the Council could veto anything against their interests.

League´s biggest problem was that they gave more importance to keep the big powers happy than being fair and punishing the agressor. Eg. Italy bombarded corfu.

The League had become a WW1 winners club and everything they did was to their own interests (especially France and Britain). It would be impossible for them to

the League had a serious conflict of interests with France and Britain and other member states. Who told the French to go when they occupied the Ruhr?

One of the biggest problems of the League of nations was it's army. It didn't have any army because no one wanted to risk their war for the League.

Maybe the sanctions could diisplease other countries, having deprived them from trade, therefore lowering their economy

The absence of the Americans deprived the League of one of the world's most important powers. Look at the video and see if you can add any other problems.