Which had the most significant impact on the department of defense budget increase between 2001 and 2014?

Between 2001 and 2014, the War on Terror, and moreover the wars in Iraq and Afghanistan, caused the U.S. Department of Defense budget to swell tremendously.  According to some estimates, between 2001 and 2014, the Department of Defense budget grew by more than seven trillion dollars from its average yearly budget in the 1990s.