Seeking to avoid the high levels of inflation that had accompanied the heavy borrowing of the American Civil War, the Wilson administration raised taxes during the war. The War Revenue Act of 1917 and the Revenue Act of 1918 raised the top tax rate to 77 percent, greatly increased the number of Americans paying the income tax, and levied an excess profits tax on businesses and individuals. Despite these tax acts, the United States was forced to borrow heavily to finance the war effort. Treasury Secretary McAdoo authorized the issuing of low-interest war bonds and, to attract investors, made interest on the bonds tax-free. The bonds proved so popular among investors that many borrowed money in order to buy more bonds. The purchase of bonds, along with other war-time pressures, resulted in rising inflation, though this inflation was partly matched by rising wages and profits.