The economic policy of the 1920s that resulted in lower taxes was the Revenue Act of 1924. This act was part of the broader trend during the 1920s, often associated with the administrations of Presidents Warren G. Harding and Calvin Coolidge, which focused on reducing taxes and government intervention in the economy. The Revenue Act of 1924 lowered income tax rates for individuals and corporations and aimed to encourage investment and economic growth.
The other options listed, such as the Emergency Tariff of 1921, the Kellogg-Briand Pact, and the Washington Disarmament Conference, were unrelated to tax policy.