The total amount the government of the United States borrowed from its various sources such as from other nations, various federal agencies and private investors etc, is known as the National Debt of U.S.
When the U.S. Government found it difficult to pay the debts in the long run, it made efforts to control the skyrocketing national debt in WWII. One such way was the selling of bonds, the government by selling bonds could get money and pay its debts
