Why did warren G. Harding win the election of 1920

Harding's campaign promised a return to "normalcy," rejecting the activism of Theodore Roosevelt and the idealism of Woodrow Wilson. Voters responded to his genial nature, impressive stature, and bland message; he won by a landslide.

By promising a "return to normalcy"

Explanation:

He promised to return the county to normalcy after World War 1, which led Harding to a landslide victory over his opponent.