"Rockoff estimates the total cost of World War I to the United States at approximately $32 billion, or 52 percent of gross national product at the time. He breaks down the financing of the U.S. war effort as follows: 22 percent in taxes, 58 percent through borrowings from the public, and 20 percent in money creation. The War Revenue Act of 1917 taxed "excess profits" -- profits exceeding an amount determined by the rate of return on capital in a base period -- by some 20 to 60 percent, and the tax rate on income starting at $50,000 rose from 1.5 percent in 1913-15 to more than 18 percent in 1918. Meanwhile, Treasury Secretary William Gibbs McAdoo crisscrossed the country peddling war bonds, even enlisting the help of Hollywood stars and Boy Scouts. The prevalence of patriotic themes created social pressure to purchase the "Liberty bonds" (and, after the armistice, the "Victory bonds"), but in practice the new bondholders did not make a tangible personal sacrifice in buying war bonds, since the yields on the set debt instruments were comparable to those on standard municipal bonds at the time. As Rockoff notes, "patriotic motives were not sufficient to alter market prices of assets during the war.""