【明報專訊】It's a scene that remains etched in our memory: huge, fast-moving airplanes crashed into the Twin Towers and, amid an outpouring of gigantic black smoke, the towers tumbled, laying waste their surroundings and leaving a scar on the American psyche (心靈).

The event

Early in the morning on 11 September 2001, hijackers of the terrorist group al-Qaeda (蓋達) took control of four planes: American Airlines Flight 11, United Airlines Flight 175, American Airlines Flight 77 and United Airlines Flight 93.

The first two planes crashed into the North Tower and South Tower of the World Trade Center (世貿中心) at 8:46 am and 9:03 am respectively. The third hit the Pentagon (國防部五角大樓) at 9:37 am, while the last plane, believed to have been targeted either at the Capitol (國會山) or at the White House (白宮), crashed into the ground in Pennsylvania at about 10 am after a fight between the passengers and the terrorists.

The attacks killed 2,996, including the 19 hijackers.

The motives

Osama bin Laden (拉登, right), who was then leader of al-Qaeda and had masterminded the attacks, said al-Qaeda's motives for the attacks included the US's support for attacks against Muslims in many places, the presence of its troops in Saudi Arabia, its support for Israel and the sanctions (制裁) against Iraq.

The responses

Soon after the attacks, the US government made a series of responses:

◆SCATANA, an emergency preparedness (戰備) plan, was invoked for the first time in US history. All aircraft were grounded and tens of thousands of passengers across the world were stranded (滯留).

◆The enactment of the USA PATRIOT Act (《愛國者法案》), which allows the US government to monitor its citizens' communications.

◆The US set up the Guantanamo Bay detention camp (關塔那摩灣拘押中心) for holding people identified as "illegal enemy combatants".

◆The US started the War on Terror. It invaded Afghanistan (阿富汗), where Osama bin Laden was reportedly hiding, and toppled its Taliban (塔利班) regime. Accusing Iraq of possessing "weapons of mass destruction" (大殺傷力武器), it invaded the Middle East country in 2003.

◆The White House announced bin Laden's death on 2 May 2011. The US Navy SEALs (美國海軍三棲特種部隊，通稱海豹突擊隊) killed bin Laden in Pakistan by President Obama's order made in April 2011 .

Long-term impacts

◆The 911 attacks marked a turning point in the US's power. They hugely impacted the US economy, and the Afghanistan and Iraq wars the country waged afterwards have left it heavily in debt. Its debt reached US$16.7 trillion in July 2013.

◆International relations scholar Simon Shen (國際關係學者沈旭暉) explains that the US was at the height of its power just before the 911 attacks happened. The US emerging as the winner of the Cold War (冷戰), its political, social, economical and cultural structures were widely regarded as the most desirable. Some scholars even thought we wouldn't see the day of US decline. The 911 attacks and the War on Terror that followed have changed all this.

◆The US being busy countering terrorism, China was spared further confrontations with the superpower. This set the country on the road to economic prosperity. It is now the world's second largest economy, leaving Japan behind.

◆Terrorism, especially that by radical Muslims, remains one of the challenges the US is faced with. To combat terrorism, the country has constantly put its airports under tight security and has maintained a number of surveillance programmes to forestall terrorist attempts.

■Think and Study

We live in a highly interconnected world. Do you think the 911 attacks have in any way affected Hong Kong or changed the course of its development? Elaborate your observations.