an organized effort on the part of workers to improve their economic and social status by united action through the medium of labor unions
The labour movement developed in response to the depredations of industrial capitalism at about the same time as socialism. However, while the goal of the labour movement is to protect and strengthen the interests of labour within capitalism, the goal of socialism is to replace the capitalist system entirely.
Answer: The Senate rejected the Treaty that was based primarily on the objections to the League of Nations. The United States wouldn't ratify the treaty and/or join the League of Nations.