Final answer:
The Pentagon was targeted on September 11, 2001, because it represents U.S. military power and was part of an attack by al-Qaeda to respond to U.S. policies in the Middle East, leading to the War on Terror.
Step-by-step explanation:
The Pentagon was an important target for terrorists in 2001 because it is a symbol of the United States' military strength and defense capabilities. On September 11, 2001, al-Qaeda, a well-organized terrorist group led by Osama bin Laden, orchestrated a devastating attack on the Pentagon, which served as a response to U.S. support for Israel and military presence in the Middle East. The attack on the Pentagon, along with the destruction of the World Trade Center in New York, signaled the beginning of the War on Terror, an international military campaign initiated by the United States and supported by many nations to dismantle al-Qaeda and associated militant organizations.