Although there are many valid criticisms that can be leveled at the United Nations (and in particular the archaic United Nations Security Council system), it at least provides the legal framework for the operation of international security. Unfortunately the US-led war on terror has done much to undermine this system - particularly with the invasions of Iraq and Afghanistan.
It has been argued by critics of the invasion of Afghanistan, that the United Nations Security Council (UNSC) never authorised the use of force in Afghanistan. The two instruments that are widely thought to have authorised the use of force are:
1. UNSC Resolution 1368 which firstly re-affirms the right to self-defence in Article 51 of the UN charter and states in clause 3:
"[The UNSC] Calls on all States to work together urgently to bring to justice the perpetrators, organizers and sponsors of these terrorist attacks and stresses that those responsible for aiding, supporting or harbouring the perpetrators, organizers and sponsors of these acts will be held accountable;"
2. UNSC Resolution 1373 imposed a duty of Member States to:
"Refrain from providing any form of support, active or passive, to entities or persons involved in terrorist acts, including by suppressing recruitment of members of terrorist groups and eliminating the supply of weapons to terrorists;"
Proponents of the invasion argue that, although the resolutions do not specifically authorise the use of military force, the harbouring of Osama bin Laden by the Taliban constituted an illegal act for which they should be held accountable. Furthermore, the right to self-defence from terrorist act would include bringing to justice the perpetrators of terrorist acts and those who provide material support to those perpetrators. However, while proponents of this argument are happy to apply it to the situation in Afghanistan, they are loathe to apply it universally.
The view that sovereign nations habouring terrorists provides a blank cheque to use military force is also held out as the reason for the ability of US forces to raid the compound in which Osama bin Laden was hiding. This action has even further damaged strained relations between Pakistan and the US which ultimately undermines the ostensible aims of the War on Terror to make the world safer. An unstable Pakistan would be disastrous, which is probably why the US has made little noise about the fact that bin Laden had been hiding in relative plain sight in Pakistan for anything up to ten years.
The problem of the raid is that its aim was not to arrest bin Laden, but to assassinate him. An arrest operation would likely have garnered less criticism - particularly if that arrest had led to a trial, either in the US or preferably before the International Criminal Court (although the US is not a signatory to the ICC). This would have sent the message that there are international crimes for which a person may be arrested and tried, rather than the message that the US can go into any country and assassinate whomsoever it pleases. One could imagine that if other countries pursued the same policies there would be uproar - and an ultimately unworkable and unstable international system.
This is why the rule of law must be applied universally. The trial before a competent court with access to a defense counsel gives authority to the decision to arrest and supports a workable international framework for dealing with international criminals. Although the ICC would be preferable, an American court would have sufficed in this instance and the potential breach of international law (although it could be argued that UNSC Resolution 1368 authorised the action) could be remedied. There has been precedent for this in the past.
The bringing to trial of international war criminals sends a message to people who would commit these types of crimes that they will be arrested and bought before the court as a common criminal, and not assassinated and martyred by a State which holds as little regard for the law as they do.