After the attacks on the US in September 2001, many commentators and political leaders declared that the world had changed for ever. Five years on, what exactly has changed?
Six writers and commentators give us their views.
Click on the links below to read what they have to say.
Ziauddin Sardar is a prominent London-based writer specialising in the future of Islam
September 11 really shook the Muslim community. As a result, Muslims have been looking at their faith much more critically and asking which tenets of Islam are axiomatic, and which can be changed or reformed.
Muslims around the world are looking at their faith more critically
In particular, issues such as the meaning and significance of the Sharia in the 21st century are now being seriously examined. Also the desirability of a theocratic "Islamic state" - the dominant idea of the late 20th century - is being questioned.
Another issue that is being hotly debated concerns the power of the religious scholars: should the authority for reinterpretation of the Koran for contemporary times be limited to a handful of scholars or should it be democratised?
In other words, should ordinary Muslims have the agency to rethink and reinterpret their faith?
Before 9/11, these kinds of questions were largely avoided. But now we are seeing them openly discussed and debated. This is not just happening in Britain, but all over the Muslim world from Indonesia and Malaysia to Pakistan and Bangladesh to Morocco and Turkey.
There has been an increase in radicalisation but radicalisation itself isn't new - it really emerged in Britain in the early 1990s. But before the attacks, few Muslims paid attention to the radicalisation of Islam.
Since 9/11, it has definitely become more entrenched and widespread. But the general trend now is to focus on the radicals, to question what they are doing in the name of Islam and to ask what can be done about rescuing Islam from their clutches. The silent majority is silent no more.
Another consequence of 9/11 is that Muslims are now very aware of globalisation and the fact that they don't live in isolation. They realise that what happens in Pakistan, for example, impacts on the community in, say, Bradford.
Chip Bok is a political cartoonist with the Akron Beacon Journal in Ohio. His work appears in most major US national newspapers and magazines. He is the author of Bok! The 9/11 Crisis in Political Cartoons.
The world didn't change on September 11, 2001. Things had already changed. The World Trade Center was bombed in 1993 by Islamist fanatics. Six people died and more than 1,000 were injured. A US military barracks in Saudi Arabia was bombed in 1996, killing 19 US troops. Al-Qaeda killed 257 when it blew up the US embassies in Tanzania and Kenya in 1998. And 17 American sailors died when the USS Cole was hit by al-Qaeda suicide bombers in Yemen in 2000.
But, because Americans have short attention spans, we were surprised that crazy people wanted to kill us on 9/11/01.
Of course, the attacks have had an effect on life here in the US, but it's been mainly political.
As of September 12, 2001, there was a tremendous outpouring of sympathy for the US and Americans felt very strongly about that. Everybody was standing together.
But this quickly began to unravel and, today, we are politically more divided than at any time in my lifetime.
The Democrats have a visceral hatred for George W Bush, which is largely to do with the fact that they are embarrassed by how America is now perceived in the world.
In terms of the day-to-day lives of ordinary Americans, very little has changed. There is certainly more security at the airports etc, but people are prepared to put up with that - they don't really complain.
In some areas, freedoms have been restricted - there is the Patriot Act and the controversy over electronic eavesdropping - but, again, most Americans are OK with that.
The attention span of the American public is very short and when nothing major happens, we just get on with life.
People are very aware that there is a simmering war going on in Iraq. But the fall-out of September 11 is not at the forefront of people's thinking.
They are thinking more about their jobs and their families. Americans desperately want everyday life to be the same as it was before 9/11.
Frank Furedi is Professor of Sociology at the University of Kent and author of Politics Of Fear: Beyond Left And Right
Since 9/11, it has become much more normal for people to represent the future in very dystopic, negative terms.
After the attacks, it became commonplace to hear politicians and commentators say that 'the world changed for ever on 9/11'. And, since then, we have become preoccupied and obsessed with the world being a more dangerous place.
The discussion about global warming has taken on the "structure of the terrorist nightmare scenario"
As a result, our anxiety has extended into ever-expanding territory. The terrorist nightmare scenario has, for example, been recycled in other areas, such as the environment. If you look at the discussion on global warming, it often has the same structure to it.
What 9/11 has done is normalised the idea that you do things just because you think there might be a problem rather than because you believe that there is a problem.
So, for example, President Bush went after Saddam Hussein because the Americans thought there was the possibility that he had weapons of mass destruction. No actual proof was required, but the fact that it might be the case was enough to go to war.
The "We haven't got time, we must do something now" psychology seems to have become institutionalised in every area of life, and there seems to be very little to distinguish between the claims and dire warnings.
This speculative reaction not only informs foreign policy but a lot of domestic policy. From climate change doom-mongers to population alarmists, every kind of fear entrepreneur is now piggy-backing on the "war on terrorism".
And, I anticipate that for some time to come, the expectation of the worst possible outcome is only going to become more powerful.
Dr Maha Azzam is the author of the report Al-Qaeda Five Years On: Threats and Challenges published by London-based think-tank Chatham House.
Al-Qaeda's popularity has waned substantially in the wider Muslim world, precisely because of its terrorist activities within the Muslim world. It has failed to win hearts and minds, as seemed to be the case immediately after September 11th.
The level of attacks in Saudi Arabia, in Jordan and the sectarian violence in Iraq have contributed to its popularity being undermined.
There is certainly a minority that finds the message and tactics of al-Qaeda appealing. And in that sense, its appeal may have even increased in the past five years. But the middle ground, which al-Qaeda was hoping to galvanise into support for its cause, has not come through.
The Iraq situation is also very particular. It's perceived as one where there is American occupation of Muslim territory, and where recruits are readily are available from neighbouring countries. Similarly, what was perceived as the American "occupation" of Saudi Arabia during the first Gulf War was rejected, and galvanised support among many.
So, when it comes to military intervention on the part of a foreign power concerning a Muslim land, much support has been galvanised for al-Qaeda. But the general public in the Muslim world has, in a sense, rejected its tactics. And this, in itself, is a disappointment for al-Qaeda.
It is still a continuing threat to America and other Western countries but it is arguable that Western governments have given Bin Laden and al-Qaeda a boost by stressing those challenges.
Richard Haass is President of the Council on Foreign Relations and author of The Opportunity: America's Moment to Alter History's Course.
September 11 changed US foreign policy in important ways. Intelligence was reoriented, counter-terrorism prioritised, homeland security elevated. The Taleban government in Afghanistan was ousted. And 9/11 created the context in which the decision to go to war against Iraq was made - a decision the full consequences of which cannot yet be measured.
US foreign policy has emphasised promoting freedom and democracy
The most enduring consequence of 9/11 for US foreign policy, though, might be in the emphasis placed on promoting "freedom".
Young men and women are thought to be less likely to become terrorists if they are participating members of societies that provide them with political and economic opportunities to live meaningful and satisfying lives.
Unfortunately, we have seen that individuals growing up in mature democracies such as the United Kingdom can still become alienated and radicalised. A more democratic Iraq has become a more violent Iraq. Elections in Palestine did not persuade Hamas to turn its back on violence; elections in Lebanon hardly dissuaded Hezbollah from initiating the crisis in the Middle East.
Meanwhile, democracy is irrelevant to those who are already committed terrorists. The goals of re-creating some 7th century caliphate or, in the case of Iraq, restoring Sunni domination are unlikely to be satisfied by free men and women openly voting.
Emphasising the need for dramatic political reform can make cooperation on other priority matters more difficult
Even if democracy were the answer, it is extraordinarily difficult to bring about. The sequencing of political and economic reform, taking into account local culture and tradition - these and other factors complicate all efforts to instil (much less install) democratic ways.
What is more, all of this social engineering necessarily takes place at the same time as the United States must call upon some of the very governments it seeks to change (and, on occasion, oust) to join with it to meet the pressing political, economic, and strategic challenges of the day.
Emphasising the need for dramatic political reform can make co-operation on other priority matters more difficult; backing off opens the United States to charges of hypocrisy and double standards. The result is that promoting democracy can be one foreign policy goal among many, but rarely should it be allowed to dominate.
Kenneth Roth is executive director of Human Rights Watch, based in New York.
It's important when speaking about the so-called war on terrorism to recognise that there are dimensions of the effort that are genuine armed conflict - there was a war in Afghanistan, there was a war in Iraq, even though at the outset it had nothing to do with terrorism.
It is also legitimate to try to prevent terrorism rather than simply prosecute those who have completed their crimes.
Russia's Vladimir Putin has used the rhetoric of the war on terror in Chechnya
But, that said, there are very disturbing dimensions to the way the Bush administration has pursued its war against terrorism.
First, because the administration has designated the war as global, it claims the right to arrest anybody any place in the world as an enemy combatant based simply on a unilateral assertion that it has intelligence linking that person to some terrorism effort.
That creates a major loophole in our criminal justice rights because the US administration claims no need to bring a suspect before a judge or to test the detention in court with actual evidence.
There are other parts of the Bush administration approach that are not directly related to its declared war but are nonetheless extremely disturbing.
The Egyptian prime minister justified his government's torture because Bush did it
It has used torture and other unlawful coercion extensively. While there is now some important backtracking with the recent announcement governing detainees in military detention, the administration reserves the right to use coercive interrogation in so far as the CIA might hold detainees in the future outside of military custody.
All of this has had the effect of lowering the human rights bar for everybody else. The United States isn't the most abusive government in the world but it is clearly the most influential.
Since 9/11, many governments have tried to exploit the war on terror and the Bush administration's approach to it to justify their own misconduct. In some cases, they have done so without even an arguable connection to terrorism.
Zimbabwe's Robert Mugabe cited his crackdown on democratic opposition as part of a fight against terrorism. Perhaps more related to terrorism - but still a stretch - Russia justifies its oppression of Chechnya in Bush terms. And China justifies its repression of the Uighur people who are seeking autonomy in Xinjiang province, in terms of the war on terror.
The Egyptian prime minister justified his government's torture because Bush did it. Israel tried to deflect criticism of its crackdown in the occupied territories by equating Yasser Arafat with Osama Bin Laden.
When a government as influential as the United States offers an excuse to ignore human rights in the name of some larger goal, unscrupulous governments around the world have been quick to exploit that fact.