Final answer:
The Department of Homeland Security, created in 2002, is the newest executive department, established in response to the 9/11 terrorist attacks.
Step-by-step explanation:
The newest executive department that was added in 2002 is the Department of Homeland Security. This department was created in response to the 9/11 attacks to centralize federal disaster response power and to federalize airport security through the Transportation Security Administration (TSA). The Department of Homeland Security is part of the executive branch of the federal government, which is composed of 15 Cabinet-level departments and numerous agencies and subunits, including the National Security Council, the Department of Defense, and the Central Intelligence Agency. Over two million civilians are employed by the federal government in a variety of capacities both within and outside of Washington, D.C.