Twenty years on from the September 11th terror attacks, the Taliban are back in power in Afghanistan.
After being driven out by US forces following 9/11, the US commitment to withdraw from the country ahead of the two-decade anniversary has resulted in Islamist rule there once again.
As the world marks 20 years since 9/11, Sky News looks at who the attackers were and how they are linked to the extremist ideology that inspired them.
Pilots and ‘muscle hijackers’
There were 19 attackers in total – split between four planes.
Four were trained pilots and each accompanied by three to five “muscle hijackers” who overwhelmed passengers and crew while they took control of their respective aircrafts.
The group, who came from Saudi Arabia, the United Arab Emirates, Lebanon and Egypt, were chosen by al Qaeda leaders in Afghanistan in 2000 before undergoing training at various camps across the country.
Those selected then travelled to Saudi Arabia to obtain US visas, before finally flying to America to await take-off on 11 September.
American Airlines Flight 11
The first plane took off from Logan International Airport in Boston and was bound for Los Angeles International Airport but crashed into the north tower of the World Trade Center at 8.46am.
Mohamed Atta, 33, Egypt
Atta was quickly identified as the ringleader of the 9/11 attacks.
The 33-year-old grew up in a strict household in Egypt where he was made to study hard. His family were not believed to be particularly religious.
After completing a degree in architecture at Cairo University he moved to Germany and enrolled on another course at the Technical University of Hamburg-Harburg.
It was in Hamburg that his religious views appear to have intensified.
He formed a prayer group for like-minded Muslims at his mosque, where he met two of the other 9/11 pilots – Marwan al Shehhi and Ziad Jarrah.
They became known as the ‘Hamburg cell’ after seeking out al Qaeda and eventually meeting Osama bin Laden.
Atta arrived in the US in the summer of 2000 and underwent flight training in south Florida.
He travelled on several commercial flights to better understand how to carry out the hijacking.
Wail al Shehri, 28, Saudi Arabia
Wail and Waleed al Shehri were brothers from Asir, a deprived region of Saudi Arabia that borders Yemen, often referred to as the “wild frontier”.
Wail was a primary school teacher in Khamis Mushait but travelled to the holy city of Medina in 2000 for help with his mental health problems.
Accompanied by his brother, the pair were redirected to Afghanistan where they were recruited by al Qaeda to take part in the 9/11 attacks.
He arrived in the US in June 2001.
Waleed al Shehri, 22, Saudi Arabia
Wail’s brother Waleed travelled with him to Medina and then to Afghanistan.
They took part in an al Qaeda training camp before acquiring US visas and travelling to America.
In May 2001 he flew with fellow hijacker Satam al Suqami from Fort Lauderdale in Florida to Freeport in the Bahamas.
The men had reservations at the Bahamas Princess Resort but were turned away due to visa issues on arrival.
He also flew solo to San Francisco in July, staying in Las Vegas for a night on the way back.
This was an unusual move as he was not instructed to take surveillance flights like some of the other attackers.
Satam al Suqami, 25, Saudi Arabia
Al Suqami was born and brought up in the Saudi capital of Riyadh.
He was studying law when he was recruited by al Qaeda along with fellow Saudi hijacker Majed Moqed to undergo terrorist training in Afghanistan.
Suqami was not considered particularly religious before his involvement with al Qaeda and had been known to drink alcohol.
Reports claim his passport was found close to the World Trade Center, with a member of the public picking it up and handing it to police shortly before the towers fell.
Abdulaziz al Omari, 22, Saudi Arabia
Al Omari was another hijacker from the poor Saudi province of Asir.
He had a degree from the Imam Muhammad Ibn Saud Islamic University and often served as an imam at his mosque.
The 22-year-old was married with a daughter.
He is believed to have been taught by the radical Saudi Cleric Sulayman al Alwan at his mosque in al Qassim province – the heartland of what has been described as the strictest form of Islam known as Wahhabism.
The mosque has been referred to by experts as a “terrorist factory”.
Al Omari was identified by his passport, which was left in luggage at the airport that never made it onto his flight.
United Airlines Flight 175
The second plane was on the same route as the first, having taken off from Logan International Airport in Boston – destined for Los Angeles.
After it was hijacked it crashed into the south tower of the World Trade Center at 9.03am.
Marwan al Shehhi, 23, United Arab Emirates
Al Shehhi was a student in the UAE before he moved to Germany in 1996.
In Hamburg at the al Quds mosque he met two of the other 9/11 pilots Mohamed Atta and Ziad Jarrah.
After offering themselves to al Qaeda and attending a camp in Afghanistan, al Shehhi arrived in Florida to do his flight training, obtaining his pilots licence in December 2000.
He was heavily involved in the planning of the attacks and took several surveillance flights to study how they would be carried out.
Al Shehhi was the youngest of the four pilots on 9/11.
Fayez Banihammad, 24, United Arab Emirates
Banihammad was one of only two Emirati hijackers.
He left his family in the UAE and travelled to the Asir region of Saudi Arabia where several of the other hijackers were from.
From there he was recruited to al Qaeda, telling his family he was going travelling to take part in relief work overseas.
He had links to one of the Saudi men who is alleged to have financed the attacks – Mustafa al Hawsawi.
Banihammad travelled to the US on a tourist visa.
Ahmed al Ghamdi, 22, Saudi Arabia
Al Ghamdi was one of four hijackers to come from the Saudi region of Al Bahah.
It is largely isolated and underdeveloped, but home to several religious tourist sites.
He left school early to fight the Russians in Chechnya where he was likely recruited to al Qaeda and then sent to Afghanistan to train.
Al Ghamdi was an imam and known as particularly religious.
He arrived in the US in May 2001 on a tourist visa.
Hamza al Ghamdi, 20, Saudi Arabia
Hamza al Ghamdi was among the youngest hijackers and came from the Al Bahah region of Saudi Arabia along with Ahmed al Ghamdi, Saeed al Ghamdi and Ahmad al Haznawi.
According to their travel records and family testimonies, the group were in contact with each other as early as 1999.
He, like Ahmed, left Saudi to fight in Chechnya and was recruited to al Qaeda there.
Hamza al Ghamdi also entered the US on a tourist visa in May, but continued to tell his family he was in Chechnya.
Mohand al Shehri, 22, Saudi Arabia
Al Shehri was unrelated to the Al Shehri brothers, despite all three being from the same region.
He like several others in the group travelled to Chechnya to fight the Russians, having failed his studies in Saudi Arabia.
Al Shehri attended a training camp in Afghanistan and was selected by al Qaeda officials to take part in the 9/11 attacks.
American Airlines Flight 77
The third flight to crash had taken off from Washington Dulles International Airport in Virginia.
It was destined for Los Angeles International Airport but hijacked over Ohio before crashing into the Pentagon in Washington DC at 9.37am.
Hani Hanjour, 29, Saudi Arabia
Hanjour was the only pilot who already had his commercial licence before being selected by al Qaeda.
He also had very good English having first travelled to the US to study at the University of Arizona in 1991.
Hanjour returned to the US to live in California in 1996 before training to become a pilot in Arizona, finally getting his licence in 1999.
He arrived back in the States for the last time in December 2000, meeting up with fellow attacker Nawaf al Hazmi in San Diego before going back to Arizona for some pilot refresher training.
They moved to Virginia in 2001 and attended the Dar al Hijrah Falls Church where the imam Anwar al Awlaki preached.
Nawaf al Hazmi, 25, Saudi Arabia
Nawaf and Salem al Hazmi were the second pair of brothers who carried out the 9/11 attacks.
He and Khalid al Mihdhar were the first attackers to arrive in the US in preparation for the hijackings.
Nawaf al Hazmi was already on the CIA’s watchlist.
He was earmarked as a potential pilot but underperformed at his flying lessons in San Diego in 2000, with leaders allowing him to stay on as a hijacker.
Al Hazmi resettled in Virginia with pilot Hani Hanjour in April 2001, before carrying out the attacks in September.
Khalid al Mihdhar, 26, Saudi Arabia
Al Mihdhar was another attacker already known to the CIA at the time of the attacks.
He had left home to fight with the Bosnian Mujahideen during the Bosnian War of the 1990s.
There he was likely recruited to travel to Afghanistan to train with al Qaeda.
He arrived in the US to train as a pilot, but like al Hazmi, fell short of requirements and was demoted to being a “muscle hijacker”.
At this point he travelled back to see his family in Yemen for a month and had to be convinced to return to Afghanistan for training.
Miihdhar was reported to have complained about life in the US before his death.
Majed Moqed, 24, Saudi Arabia
Moqed was from a small town called Al-Nakhil, west of Medina, in Saudi Arabia.
He was studying law at university when he was recruited to Afghanistan to train with al Qaeda.
Moqed was friends with Satam al Suqami, who was a hijacker on the first 9/11 flight.
He arrived in the US in May 2001 and helped plan the attacks in the months before they were carried out.
Salem al Hazmi, 20, Saudi Arabia
Salem al Hazmi was the younger brother of Nawaf, who was a hijacker on the same flight as him.
His family, from the Al Bahah region, claimed he was a difficult teenager and not particularly religious.
A member of al Qaeda said his brother Nawaf pleaded with Osama bin Laden to let him take part in the attacks.
He arrived in the US on a tourist visa in June 2001 and settled in New Jersey before 11 September.
United Airlines Flight 93
The fourth and final plane involved in the 9/11 attacks had taken off from Newark International Airport in New Jersey bound for San Francisco International Airport.
It was hijacked and headed towards Washington DC, but passengers managed to overcome the attackers and crash land in a field in Shanksville, Pennsylvania.
Ziad Jarrah, 26, Lebanon
Jarrah was the only hijacker to come from Lebanon.
He grew up in a secular household but moved to Hamburg, Germany in the 1990s where he met two of the other pilots Mohamed Atta and Marwan al Shehhi.
They formed what became known as the Hamburg cell and joined al Qaeda.
He arrived in Florida to train as a pilot in the summer of 2000 but returned to Germany to see his girlfriend after getting his licence.
It was reported that Jarrah changed his mind about the plot while he was away from the US.
Ramzi bin al Shibh, another member of the Hamburg cell, is believed to have convinced him to go through with it.
He had prepared to travel to the US to get his pilots licence but was refused a visa.
Jarrah was identified by his passport, which was found at the crash site.
Saeed al Ghamdi, 21, Saudi Arabia
Al Ghamdi was also from the Al Bahah region of Saudi Arabia.
He shared the same tribal affiliations as Ahmed al Ghamdi, who was on the second plane, and Ahmad al Haznawi, who was on the same plane.
Al Ghamdi, like several others, dropped out of education to fight the Russians in Chechnya and was rediverted to Afghanistan to train with al Qaeda.
He arrived in the US in June 2001, practicing for the attacks in Florida.
The 21-year-old was identified by his passport, which, along with Jarrah’s, was discovered at the crash site.
Ahmad al Haznawi, 20, Saudi Arabia
Al Haznawi came from the isolated Al Bahah region of Saudi Arabia.
Like many of his contemporaries he fought in Chechnya, where he was sent to Afghanistan for an al Qaeda training camp.
He arrived in the US in June 2001 and lived in Florida while he prepared for the attacks in September.
Ahmed al Nami, 23, Saudi Arabia
Al Nami was born in the impoverished Asir region of Saudi Arabia.
He had trained in announcing the call to prayer and left his family to go on the Hajj pilgrimage in 2000 but never returned.
After being recruited by al Qaeda he went to an Afghan training camp where he met the al Shehri brothers and Saeed al Ghamdi, who was also on his plane.
He arrived in the US in May 2001 on a tourist visa and lived in Florida ahead of the attacks.
Al Qaeda and the Taliban
Osama bin Laden
Osama bin Laden founded al Qaeda in 1988 after fighting against the Soviets with the Mujahideen in Afghanistan.
He was from a wealthy Saudi family but settled in Afghanistan after the conflict to set up a base for his jihadist group.
The Taliban ruled the country for five years between 1996 and 2001, during which time its leader Mohammed Omar formed ties with bin Laden as he plotted an attack on the US.
Although their ideologies differed, both groups’ beliefs were rooted in extreme Islam and a hatred of the West.
The Taliban were ousted during President George Bush’s War on Terror but are back in power following the US withdrawal in August.
Although bin Laden was killed in an operation by the Obama administration in 2011, and the Taliban has promised not to allow al Qaeda into the country, many of their current ministers are linked to the old regime.
Mohammad Hasan Akhund – acting prime minister
Mohammad Hasan Akhund is from Kandahar, the birthplace of the Taliban and former home of al Qaeda’s Al Farouq training camp, where several of the attackers prepared for the 9/11 attacks.
He is also an associate of former Taliban leader Mohammed Omar, who had longstanding links with bin Laden before 2001.
Khairullah Khairkhwa – acting culture and information minister
Khairullah Khairkhwa was captured by the US following the attacks in 2001 and detained at Guantanamo Bay.
He was released in 2014 and is now back in power.
The former governor of Herat province has long been accused of being a close associate of bin Laden and other al Qaeda members, something he denies.
Mohammad Yaqoob – acting defence minister
Mohammad Yaqoob is Mohammed Omar’s son.
His father had developed close ties with bin Laden in the years before 9/11.
Yaqoob’s family connections with the former Taliban give him extremely high rank in today’s organisation.
He is also thought to have had the backing of Saudi Arabia throughout his military career.
Abdul Ghani Baradar – acting deputy prime minister
Abdul Ghani Baradar co-founded the Taliban movement.
He is the only surviving group leader to have been personally appointed by Mohammed Omar – bin Laden’s associate-turned rival.