The following chart shows federal outlays and revenues from 1940 to the proposed levels in 2009. The difference between the two equals the federal deficit or surplus.
Aside from specific policy initiatives, spending grows over time in order to accomodate a larger economy and population. Though many federal programs were cut during the 1990s, the outlays continued to increase as more people retired and Social Security payments grew. Recent growth in spending is due in large part due to increases in military spending.
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Source: Office of Management and Budget, Budget of the U.S. Government, FY2009, Historical Tables [1].
Links:
[1] http://www.whitehouse.gov/omb/budget