It was Wilson's hope that the final treaty would have the character of a negotiated peace, but he feared that the passions aroused by the war would cause the Allies to make severe demands. In this he was right. The concept of self-determination proved impossible to implement. Persuaded that his greatest hope for peace, the League of Nations, would never be realized unless he made concessions to the Allies, Wilson compromised on the issues of self-determination, open diplomacy and other specific points during the peace negotiations in Paris. However, he resisted the demands of the French premier, Georges Clemenceau, to detach the entire Rhineland from Germany, prevented France from annexing the Saar Basin, and frustrated a proposal to charge Germany with the whole cost of the war -- although the Versailles Peace Treaty did levy a heavy burden of reparations upon Germany.
In the end, there was little left of Wilson's proposals for a generous and lasting peace but the League itself -- and the president had to endure the final irony of seeing his own country spurn League membership. Partly due to his own poor judgment at the time, Wilson made the political mistake of failing to take a leading member of the opposition Republican Party to Paris on his Peace Commission. When he returned to appeal for American adherence to the League, he refused to make even the moderate concessions necessary to win ratification from a predominately Republican Senate.
Having lost in Washington, Wilson carried his case to the people on a tour throughout the country. On September 25, 1919, physically ravaged by the rigors of peacemaking and the pressures of the wartime presidency, he suffered a crippling stroke at Pueblo, Colorado, from which he never fully recovered. In March 1920, the Senate rejected both the Versailles Treaty and the League Covenant. As a result, the League of Nations, without the presence of the United States or Russia, remained a weak organization.
Wilson's belief in a moral and legal basis for war and peace had inspired the nation. However, when events didn't live up to this optimistic standard, Wilsonian idealism gave way to disillusion, and the nation withdrew into isolationism.
Source: U.S. Department of State