War has been a constant feature of human life since the beginning of civilization. Over time, however, statesmen have sought to regulate the conduct of hostilities and to make it harder, at least in theory, to initiate new wars. With the foundation of the United Nations, it was clear that the intent was to prevent another World War and to make war as far from the conduct of international relations as possible.
Conflict and war have been constant features of human life since the beginning of humanity and civilization. Whether it was city-states, such as Athens and Sparta, fighting one another, or a big Empire, such as the Roman Empire, waging war to conquer more territories and extend its borders, wars have been ever-present in history books and literature.
Over time, however, statesmen and military leaders have sought to regulate the conduct of war, both in terms of the weapons allowed to fight in them and of the circumstances which make war a lawful solution to national, and most importantly international disputes. Most of these developments, which are quite recent (starting in the nineteenth and early twentieth centuries), have become customary international law principles. Some of these efforts are also included in specific articles in one of the most fundamental international law documents, the UN Charter, which make war not legal or legitimate in international law in most situations.
In fact, according to the UN Charter, war is only considered legal and legitimate when its purpose is self-defense: Article 51 of the Charter states that “nothing in the […] Charter shall impair the inherent right of individual or collective self-defense if an armed attack occurs against a Member of the United Nations.” This provision constitutes the only explicit international law exception to the general rule laid out in Article 2(4) of the Charter, according to which “all Members shall refrain in their international relations from the use of force against the territorial integrity or political independence of any state, or in any other manner inconsistent with the Purposes of the United Nations.”
Despite the general prohibition of the use of force and war in the UN Charter, there is a chance for the United Nations themselves to authorize the use of force against a state if its government is violating international law and the principles of the UN Charter and all peaceful means of solving the dispute have failed. In fact, the UN Security Council has the ability, under Chapter VII of the UN Charter (Articles 41 and 42), to authorize UN Member States to intervene militarily on behalf of the UN. An example of this was the case of the 1991 Gulf War against Iraq after its government invaded Kuwait, when the Security Council authorized, with Resolution 678, the formation of a coalition of the willing to use “all necessary means” to roll back the Iraqi invasion.
With the recent increased polarization within the Security Council, however, it has become harder and harder to obtain such authorizations, even when the international law violations being committed are evident and documented, for instance during the genocide in Rwanda in 1994 or currently in Syria and Myanmar.
The question whether war is legal or not, then, follows almost naturally. The answer, however, is everything but simple or straightforward: international humanitarian law, the part of international law that deals with conflicts and their regulation, does not provide specific thresholds to define what an armed conflict is or what triggers the provisions regulating it. Furthermore, there is hardly any way of enforcing the same regulations and hold the violators accountable.
This particular question about the legality of law is even more complicated because of instances in which the Security Council has “condoned” military intervention which had not been authorized by its own vote after they happened. For instance, during the war in Kosovo in 1998-1999, NATO conducted unauthorized airstrikes against Serbian forces which the Security Council later labeled “illegal but legitimate.”
Although this only happened in the framework of a humanitarian intervention to save the people of Kosovo from ethnic cleansing, it still constitutes a precedent that has the potential to be cited to justify other kinds of military interventions. The evolution of humanitarian intervention in the norm known as Responsibility to Protect (R2P), which allows states to intervene, unilaterally or multilaterally, to protect people whose human rights are being violated by their own government.
While the norm is not necessarily used as often as it could be, it has gained almost universal recognition and has quickly become a customary international law principle which represents yet another exception to the prohibition of the use of force.
The advent of cyber weapons has been further complicating the debate on the legality of law, mostly because there are no formal international law provisions which have been widely agreed upon and they have not been inscribed in customary international law yet. This is because cyber weapons are the newest, most recent form of weaponry, and it is hard to adapt them and their effect to the regulations intended for more conventional weapons and their effects.
Despite the terrible nature of war in general and the dire consequences it creates, and despite the many efforts to regulate it and restrict its lawful use in the conduct of international relations, it is still widely used as a means to solve international disputes. The existence of inherent exceptions makes it harder to enforce the prohibition of the use of force, especially considering the increased polarization in the international scenario.