Original Cost: $551 billion
Inflation Adjusted Cost: $597 billion
After the Sept. 11, 2001, terrorist attacks, President George Bush declared a new War on Terror with the stated objectives of securing the homeland and disrupt the international terrorist networks. In October 2001, the US and its allies launched Operation Enduring Freedom and invaded Afghanistan. On March 20, 2003, the second Iraq War began as the reports alleged that Iraq had amassed weapons of mass destruction that threatened the US and its allies.