The UN Charter prohibits the threat or use of force ‘against the territorial integrity or political independence of another state’. There are two exceptions set out in the Charter: first, if the use of force is necessary in self-defence (either for a state’s own defence or to defend another state at its request), and second, if it is authorized by a Security Council resolution.
In the case of the UK intervention against IS in Iraq, the Charter’s prohibition is not triggered: the Iraq government has requested military assistance from the coalition to fight IS within its borders. In the House of Commons last Friday, the prime minister stated that ‘[t]here is a clear legal base for UK military action to help Iraq defend itself from ISIL’; the Iraqi government had requested UK help and given ‘clear consent’ for UK military action. ‘We have the letter from the Iraqi Government to the UN Security Council, we have the public statements from Prime Minister Abadi and President Masum, and we have the personal requests made to me and to the full UN Security Council by Prime Minister Abadi in New York on Wednesday,’ he said.
Whatever the arguments against the military intervention made in the Commons on other grounds, there is no obstacle under international law to the military action. This is a situation very different from the last UK intervention in Iraq in 2003, where the legality was strongly contested. A government is entitled to invite foreign military to assist in quelling attacks from violent groups within its borders threatening that country’s peace and security. While this entitlement may be challenged where the government has lost territory and democratic support, this is not the case with the recently reconstituted government in Iraq.
The position will be different if the UK wishes to take part in the coalition engaging in military intervention in Syria. Here, the use of force would come up against the prohibition in the UN Charter and requires legal justification. While it appears that President Assad is being informed of the US airstrikes, any such implicit acceptance of the strikes could not constitute an invitation for outside military assistance. Nor does the fact that a number of states dispute the legitimacy of Assad’s regime mean that in international law his government is no longer entitled to speak for Syria; the recognition of governments depends upon effective control.
So, in the absence of a resolution from the Security Council authorizing military action in Syria against IS, would military intervention by the UK be legally justifiable? The prime minister has said that it would be, referencing collective self-defence against IS in respect of its attacks on Iraq and averting a humanitarian catastrophe. The US in its letter to the UN secretary-general of 23 September relied on self-defence to justify its own actions in Syria: the defence of Iraq in the case of IS, and the defence of the US and its allies in respect of actions against the Al-Qaeda associated Khorosan Group.
If the UK were to justify intervention in Syria on the basis of self-defence, the government would need to show that either the action was being taken in support of Iraq, or it was in defence of the UK. In either case that would depend on the facts, but individual acts of horror against a very few of a state’s nationals would not at first sight justify the use of military force in another country. In both cases military action must be shown to be necessary to avert an actual or imminent attack and proportionate to that need. A further problem relates to the fact that military intervention in Syria would not result from the acts of the Syrian government itself but from an armed group or groups in that country. There is growing international support for the argument that self-defence can be used not only against a threat or attack from another state but also against an armed group within a state if that state is unable or unwilling to deal with the threat from the armed group; but the argument is not uncontroversial.
An alternative – and even more controversial – justification for the use of force would be humanitarian intervention. The ‘responsibility to protect’ doctrine makes clear that in the first place it is for the government of a state itself to protect its own people. If that duty is not fulfilled, the international community has a responsibility to act. However, the 2005 UN General Assembly resolution which endorsed the responsibility to protect doctrine reiterated the role of the Security Council in authorizing military action in such circumstances. Most governments of the world do not agree that the doctrine authorizes the use of military force in the absence of a Security Council resolution. The UK government is one of the few that asserts otherwise.
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