Question: The 2010 Pentagon shooting was an attack upon the headquarters of which U.S. department?

Context paragraphs:
War Powers Resolution: The War Powers Resolution (also known as the War Powers Resolution of 1973 or the War Powers Act) (50 U.S.C. 1541–1548) is a federal law intended to check the president's power to commit the United States to an armed conflict without the consent of the U.S. Congress.  The Resolution was adopted in the form of a United States Congress joint resolution.  It provides that the U.S. President can send U.S. Armed Forces into action abroad only by declaration of war by Congress, "statutory authorization," or in case of "a national emergency created by attack upon the United States, its territories or possessions, or its armed forces."

Spafford Farm massacre: The Spafford Farm massacre, also referred to as the Wayne massacre, was an attack upon U.S. militia and civilians that occurred as part of the Black Hawk War near present-day South Wayne, Wisconsin.  Spafford Farm was settled in 1830 by Omri Spafford and his partner Francis Spencer.

2010 Ayn clashes: The 2010 Ayn clashes saw Ethiopian and Somaliland forces engage Dulbahante clan militia in Puntland's Ayn region in a bid to reconquer the region ahead of the Somaliland presidential election, 2010.  The battle was prompted by Ethiopian troops seizing a truck belonging to the Dulbahante, sparking a Dulbahante response and Ethiopian retaliatory attack on Buuhoodle and a Somaliland attack upon Widhwidh.  More clashes were reported to have occurred near Widhwidh on 19 July 2010.

Bars Fight: Bars Fight is a ballad written by Lucy Terry.  The ballad is about an attack upon two white families by Native Americans on August 25, 1746.  The attack occurred in an area of Deerfield called "The Bars", which was a colonial term for a meadow.  The poem was preserved orally until it was published in 1855 in Josiah Gilbert Holland's "History of Western Massachusetts".

Military Professional Resources Inc.: L-3 MPRI, was a global provider of private military contractor services.  It offered a wide range of professional services to both public and private customers, most notably the U.S. Department of Defense, the U.S. Department of State, the U.S. Department of Justice, U.S. Department of Homeland Security, Law Enforcement organizations, foreign governments, government agencies and commercial businesses.

Pentagon Force Protection Agency: The Pentagon Force Protection Agency (PFPA) is an American law enforcement agency within the U.S. Department of Defense (DoD) charged with protecting and safeguarding the occupants, visitors, and infrastructure of The Pentagon, the Mark Center Building, the Defense Health Headquarters, and other assigned Pentagon facilities.

The Pentagon: The Pentagon is the headquarters of the United States Department of Defense, located in Arlington County, Virginia, across the Potomac River from Washington, D.C. As a symbol of the U.S. military, "The Pentagon" is often used metonymically to refer to the U.S. Department of Defense.

Japanese submarine I-23: I-23 was a Type B1 submarine of the Imperial Japanese Navy during World War II.  After a raid on the West Coast of California she participated in an attempt at a second attack upon Pearl Harbor.  After surviving an American air attack on Kwajalein "I-23" was lost in early 1942 with all hands somewhere off the Oahu coast of Hawaii.

Transition Assistance Program: The Transition Assistance Program (TAP) is a U.S. Department of Defense-led program that provides service members with information and resources to prepare them for their civilian life.  TAP is an interagency program between the Department of Defense (DoD), U.S. Department of Labor, Department of Veterans Affairs, Small Business Administration, U.S. Department of Education, and Office of Personnel Management.  Service member participation in TAP is mandatory.

2010 Pentagon shooting: On March 4, 2010, John Patrick Bedell shot and wounded two Pentagon police officers at a security checkpoint in the Pentagon station of the Washington Metro rapid transit system in Arlington County, Virginia, just outside Washington, D.C. The officers returned fire, striking him in the head.  He died a few hours later the next day.

Supporting paragraphs: 2010 Pentagon shooting The Pentagon
Answer: the U.S. Department of Defense