The graph below shows the rise and fall of spending in the government-defined function area of "national defense" over the past three decades. After declining in the 1990s, a renewed military build-up has taken place from 2001 onwards. Note that definitions of military spending usually include a broader array of spending such as military assistance which is not included in the graph below.
Source: Office of Management and Budget, Budget of the U.S. Government, FY2007, [1] Historical Tables, Table 5.1 and put in $2006 by using deflators in Table 10.1.
Links:
[1] http://www.whitehouse.gov/omb/budget/fy2007/