The major feature of earlier US history that worked to keep the US out of the League of Nations was the idea that it had tended to get burned by involvement with Europe. In other words, when it got involved in European struggles, things tended to go badly for the US.
One example of this would have been the US involvement in the Napoleonic Wars between France and England. When the US got sucked into this dispute, it ended up almost going to war with France and finally actually going to war with England in the War of 1812. A similar thing happened in WWI.
So the US did not want to be involved with European affairs because it did not want to be dragged into another war.