WW3?
If we are in the pre-amble to WW3, the immediate question must be, who will be on the opposing sides? It surely isn't going to be conventional forces v conventional forces.
The real problem to the current world situation is that the US seems to believe that there is a conventional military answer to the terrorist threat. However, as the British demonstrated in Northern Ireland, commited terrorists are hard to defeat using purely conventional forces because of the nature of terrorism and how they fight. What does defeat terrorism is to rigidly apply the Rule of Law in a way that all perceive to be impartial. This will then remove their support from the population within which they reside. This is admittedly far harder with international terrorism than against the IRA or the Mau Mau, who work within a known territory, but the principle should still be sound. We also need to work to achieve long term solutions that the international community understands to be as fair as possible. If it is not thought to be fair, someone will keep fighting and these days that means fighting dirty.
For me the real answer is that we need to turn back to the United Nations and prevent the US from undermining their work. The UN was formed for very good reasons post WW2. It is not perfect but it has far more international credibility than the US as it is mostly democratic, with each sovereign nation having a vote. The current world situation is as much a result of the lack of perceived international credibility for the US policy on Iraq than any other factor. After all, had the UN clearly stated that we should go into Iraq I doubt that we would have had a million people marching through London protesting. Once again, the UN may not have all of the solutions but the US policy has probably exacerbated international terrorism, not solved it.
If the international community is serious about achieving a long term solution we would be addressing some of the inequalities in the world and helping those nations whose people are starving or dying prematurely because of lack of resources. If we started building engineering and medical schools in Afghanistan and allowed the people there to become more self sufficient and help themselves, they may turn away from other solutions to their problems. Killing people who feel that they are defending their way of life creates long term problems. If you want proof of this ask yourself why the result of the Battle of the Boyne in 1690 is still relevant to the people of Northern Ireland today!
Lastly, the fact that 15 of the 19 terrorists responsible for destroying the WTC were from Saudi Arabia is still hugely significant. To the young disaffected men of that country there is a basic disconnect between the teachings of the Wahabi strain of Islam and the reality of what they see in their own country. They are told that their religion and beliefs are superior to non-Muslims yet their nation has been unable to defend itself against another arab nation (post the Iran-Iraq War and through the 1990s). Defence of Saudi Arabia has been aided by having large numbers of US forces, who are of course the infidel, based on Muslim territory. What they have been told does not relate to what they see. Their answer seems to be to attack the US and the western way of life. Remembering that the first WTC attack was back in 1993 shortly after the 1991 Gulf War.
This is my understanding and may be an overly simplistic view of a complicated situation. However, the might of the US military and intelligence community have yet to come up with real results on the ground in Iraq and Al Qiada are still active.