The most accurate response is:
Division over joining led to a standstill in the Senate, which prevented the U.S. from ratifying the Treaty of Versailles.
This division primarily stemmed from a lack of consensus among senators, which prevented the ratification needed for the U.S. to join the League of Nations established by the Treaty of Versailles. Although there were other factors involved, including political opposition and concerns about entangling alliances, the deadlock in the Senate was the primary reason for the U.S. not joining the League.