Final answer:
The September 11, 2001, attacks by Al-Qaeda terrorists triggered the 'War on Terror' and reshaped U.S. national security strategies.
Explanation:
The September 11, 2001, attacks against the United States carried out by Al-Qaeda terrorists resulted in the hijacking and crashing of four passenger planes on the East Coast, leading to significant loss of life and property damage.
These attacks marked the beginning of the 'War on Terror,' a military campaign aimed at combating terrorist organizations like Al-Qaeda, ultimately involving military actions in Afghanistan and Iraq.
The events of 9/11 profoundly impacted U.S. national security policies and led to increased focus on counterterrorism efforts worldwide.
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