- Armed conflicts and attacks
- September 11 attacks
- Planes are hijacked by members of a terrorist group. They flew into the World Trade Center in New York City, The Pentagon, and a field in Pennsylvania, killing about 3,000 people including 19 of the terrorists. The hijackers were Islamic terrorists from Saudi Arabia and several other Arab nations. Reportedly financed by the al Qaeda terrorist organization of Saudi fugitive Osama bin Laden, they were allegedly acting in retaliation for America’s support of Israel, its involvement in the Persian Gulf War and its continued military presence in the Middle East. Meanwhile, a fourth California-bound plane United Flight 93 was hijacked about 40 minutes after leaving Newark Liberty International Airport in New Jersey. Because the plane had been delayed in taking off, passengers on board learned of events in New York and Washington via cell phone and Airfone calls to the ground.*
- Reactions to the September 11 attacks
- Canada's border with the United States is on high alert in the aftermath of the terrorist attacks in the United States so the Canadian government initiates both "Operation Support" and "Operation Yellow Ribbon."
- Early speculation about the source of the attacks centered on Saudi-born terrorist leader Osama bin Laden, who was living in and working from Afghanistan. Islamic Emirate of Afghanistan leaders condemned the attacks and rejected suggestions that Osama bin Laden could be behind them.
- Prime Minister of the United Kingdom Tony Blair cancels a speech he was due to give to the TUC, and pledges to "stand shoulder to shoulder" with the United States.