attacks in New York City, Washington D.C., and Shanksville, Pennsylvania, United States, killed 2,993 people.
anthrax attacks kill 5 and infect 17 others by anthrax spores in New York City, New York, Boca Raton, Florida, and Washington D.C. in the United States.
the War in Afghanistan begins.
Operation Active Endeavour officially begins.
Operation Enduring Freedom – Philippines begins as part of Operation Enduring Freedom in the Southern Philippines.
the Georgia Train and Equip Program begins.
Operation Enduring Freedom - Horn of Africa begins.
anti-war groups across the world organized public protests against war with Iraq. About 36 million people across the globe took part in almost 3,000 protests.
Colin Powell addressed a plenary session of the United Nations Security Council, stating categorically that Saddam Hussein was working to obtain key components to produce nuclear weapons.
the Iraq War begins. President George W. Bush refers to it as "the central front in the War on Terror".
Saddam Hussein is found and captured by U.S. forces.
The Georgia Train and Equip Program ends, but military assistance to Georgia continued through the Georgia Sustainment and Stability Operations Program.
The United States government, led by the Central Intelligence Agency's Special Activities Division, begins a series of ongoing attacks on targets in northwest Pakistan using drones (unmanned aerial vehicles). These attacks sought to defeat the Taliban and Al-Qaeda militants who were thought to have found a safe haven in Pakistan.
the 1st London bombings kill 52 people and injure 700 more.
the Operation Enduring Freedom – Trans Sahara begins.
Newly elected Obama administration has stopped using the phrase "war on terror"; John Brennan announces that the U.S. is "at war with al Qaeda", not involved in a "global war on terror"
Osama bin Laden is killed in a raid by United States Navy Seals on his residence in Pakistan.
Tsarnaev brothers Dzokhar and Tamerlan, aged 19 and 26 respectively, exploded bombs at the Boston Marathon on Monday, April 15. There were three casualties, one including an eight year old boy. On Thursday, April 18, the government released photos of the two suspects. That night, a firefight erupted between the brothers and the Boston police. Tamerlan was killed in the firefight, but Dzokhar escaped. A manhunt was conducted the next day and at night on Friday April 19, Dzokhar was captured and taken into custody after being discovered hiding in a boat in Watertown, Massachusetts.