The L.O.N had witnessed Japan invade Manchuria (in China) in 1931 to its satisfaction. So Italy thought the League of Nations could not stop her when she invaded Ethiopia. Ultimately the LON failed to stop Italy invading Ethiopia in 1935.
The Hoare Laval pact in which the two foreign ministers of Britain and France respectively encouraged Italy to take over Ethiopia they resolved that the Northern part of Ethiopia be taken by Italy and the South for Haille Sellassie. This was a complete sale out of Ethiopia and since Britain and France were the major powers in the League Italy inevitably took over Ethiopia.
The LON put up weak arms embargos on the two belligerent countries. The embargo only worked to weaken Ethiopia. Even most countries still traded with Italy when LON was watching.
The major powers which would have assisted Ethiopia were not allowed to join the League and if they did they were expelled. Germany joined in 1926 and withdrew in 1934; USSR joined in 1934 and withdrew in1939 at a time when she would have been of help to Ethiopia. USA could not join because of her isolationist policy. The League therefore missed ideas of the power full countries before and after the crisis.
By the time of the crisis, the League was in a deep economic abyss (depression) 1929 to 1934, thus could not have any assistance from the member states. The European states which dominated the League just played an observers role and swore not to intervene.
The reluctance and negligence of the major powers to act; Britain and France did nothing because Ethiopia was regarded insignificant. They thought the invasion would take few days and knew that the outside world could not condemn the act. They were dismarred when the crisis turned into a war and later received public outcry and condemnation throughout the world.
The League feared to antagonize Mussolini so as to keep him as an ally against the real danger German which was under Adolf Hitler. They feared an alliance between Italy and Germany both at home and in Africa. In this way no European member of the League would dare to assist Ethiopia.
Disunity among the member states of the League especially before and after the out break of World War II. They could not reach decisions on crucial occasions so when the attack occurred there was no need to sermon them since nobody would appear and take it serious or implement procedures. This made the League very weak to act.
The League lacked a collective command military force of its own to confront Mussolini when he attacked Ethiopia. No member was willing to dispatch her troops to assist Ethiopia hence the league just watched Mussolini rape Ethiopia.
The other members of the League were also expanding and attacking other states. But in all these cases the League was watching powers like Britain, France in the political game so it could not condemn the attack of Italy on Ethiopia thus reducing any possibility of the LON to avert the war.
The failure of the world disarmament conference 1932- 33 could have made the League impotent over the issue. Germany demanded equality with France in armament but France wanted her given eight years, Germany withdrew from the conference and the League could not enforce the membership of any country thus making them pursue their own policies giving Italy the impetus to attack and occupy Ethiopia.