How did the United States respond to the events of September 11, 2001?

A by increasing the size of its nuclear weapons stockpile

® by ending its economic partnerships with former Soviet countries

© by adopting isolationist policies to insulate itself against further aggression

• by pursuing military action in countries that were accused of supporting terrorists

By pursuing military action in countries that were accused of supporting terrorists. The United States launched the War on Terror, which included invading Afghanistan (where Al-Qaeda was based) and later Iraq. Additionally, the U.S. implemented new security measures, such as the establishment of the Department of Homeland Security and the implementation of the PATRIOT Act, to prevent future terrorist attacks.