Answer:
he League of Nations was a-ctua-lly one of fourteen major points proposed by President Woodrow Wilson in order to end the possibility of war. However, opposition by the British Empire and France whittled the Fourteen Points down to just the League of Nations. The principles that were meant to guide it and empower it, such as self-determination and freedom of the seas, were rejected in favor of provisions designed to punish and alienate the Germans. Finally, the United States -- the major supporter of the League of Nations -- refused to ratify the treaty that created it.
So you can see that it was hamstrung from the very beginning. It has no enforcement power.
Compare that with the United Nations. From its inception it had at least the tacit support of every major nation. The Allied Powers of WW2 (Britain, America, France, China, and the Soviet Union) would often describe themselves as the United Nations and after the war when the UN was officially created they formed the nucleus of its Security Council. The UN had a lot of funds, hardware, and political support, which it was able to employ when the international community decided someone was a threat. For example, in the Korean War the troops who fought against North Korea fought under the flag of the United Nations. Later on, the UN was able to intercede and mediate in conflicts such as the Indo-Pakistani conflict and the administration of the ex-colonies of Japan and Nazi Germany. Granted, the UN is far from perfect, but it has much more prestige and resources than the League ever got.