President Woodrow Wilson knew the importance of the League of Nations and the Treaty of Versailles. The Senate did not want to approve the Treaty because they thought it would make the US lose some of its independence and freedom.
He wanted the Treaty to be accepted by the Senate as it was written and he would not make any compromise. The Senate said that if the president accepted some changes the treaty would pass.
The president refused, accepted no compromise and the Treaty was defeated by seven votes in the Senate, this way if Woodrow worked with the Senate and made some changes, possibly the Treaty would have passed.