Was the UK's invasion of Iraq in 2003 defendable under international law or is it a war without a substantiated casus belli?

In March 2003, in response to the 9/11 attacks and reports of WMDs (weapons of mass destruction), the US launched Operation Iraqi Freedom, which the UK joined. Unlike the first invasion of Iraq in 1991, this coalition was not sanctioned by the UN. Was the UK, under international law, justified to carry out a full-scale invasion which would lead to one million Iraqi deaths? No. An extremely unjustified invasion, given that diplomacy had not been exhausted or, if action was necessary, did not require a full-scale invasion. This article will examine the justification provided for the war, as well as the criticisms and legal issues it raised. 

Firstly, their justification leading up to the war, the UK had stated that it had revived Resolution 678, which, since 1990, with Resolution 1441, insinuated it could be invoked again after the Iraqi occupation of Kuwait had ended. Along with this, the UK alleged that the invasion was to eliminate a regime connected with the terrorist organisation Al Qaeda. The government argued that it was, in fact, a defensive war after the 9/11 attacks on the United States, and as the UK is a key ally, it was obliged to defend its ally. This is legally dubious, however, with Resolution 678 not actually authorising military force in the first Gulf War, rather requesting that a peaceful solution to the Iraqi invasion of Kuwait be found to end the occupation.  Secondly, the terrorist attacks on US soil were not at the behest of Iraq or its government, displaying that it cannot be considered a first strike on the US. While the general secretary of the UN called it “illegal”. 

A second justification made by the United States is that the Invasion was, in fact, pre-emptive self-defence against Iraq, again citing Iraqi alleged cooperation and friendship with Al-Qaeda. This use of Article 51 in the UN charter cites self-defence. However, this very much stretches the fabric of Article 51, because Iraq posed no immediate threat to the United States. The Prime Minister Tony Blair hinted at the time that this was a humanitarian mission designed to free the Iraqi people. If this were true, then such an intervention would require a Security Council sanction to legitimise the operation. Along with this, there had to be a clear intention of mass atrocities. This evidence was not apparent at the time of the invasion, so there was no pretence to it.  

In conclusion, the UK stretched the legal framework to justify the 2003 invasion of Iraq, which, in the end, was still rejected by international law. While this displays that the UK did, in fact, violate international law, it has also highlighted international law’s fragility and its ineffectiveness at resolving conflicts.