War is an enduring feature of human life. In recent times it has become more common for people from many different countries and cultures to fight each other in the name of national or personal interests. Such fighting is often characterized by the use of weapons that are increasingly accessible, more varied and more destructive. It is also often accompanied by non-lethal means of attacking individuals and groups, such as cyber attacks or improvised explosive devices, in addition to traditional methods like air strikes and bombing.

Even a casual look at the costs of modern wars reveals that they can be very high. The US has borrowed trillions of dollars to fund its current wars, which will have to be paid back with interest over the long term, and its veterans have incurred very high levels of physical and mental harm. Some of them will require medical care and other assistance for decades after their wars have ended, and their families will suffer as a result.

But there is another cost of war that goes beyond the financial and monetary: The emotional, psychological and physical toll on those who fight it. Soldiers experience this in the form of trauma, fear and anxiety, which can have a lasting impact on their lives and health. Civilians suffer at the hands of combatants, who may commit atrocities and abuses in addition to killing civilians, especially women and children. In addition, many civilians are forced to flee from their homes, and this can have significant implications for the security of nations, including their economic growth and stability.

As a result of this complexity, it is difficult to construct a precise definition for war. Various sub-disciplines of history, politics and military studies have wrestled with this question in a variety of ways. However, examining the internal logic of each of these attempts often shows that they are a reflection of broader philosophical positions: Cicero defines it as “a contention by force”; Hugo Grotius states that it is a “state of war”, a conflict between opposing forces; Karl von Clausewitz writes that “war is nothing more than politics by other means”.

While such definitions provide valuable guiding principles, they do not adequately capture the full complexity of real war. This is mainly because real war involves interaction between belligerents over a period of time, with decisions made at tactical, strategic (campaign) and national levels. In addition, chance events and friction are enduring features of war, whether it manifests as equipment malfunctions, civil-military disagreements, misreading intelligence or simple misunderstandings between adversaries.

To be effective, warfare must be conducted in a manner that takes into account all of these factors. This is a challenge that is likely to remain with us into the foreseeable future, as people seek protection or the acquisition of critical resources, the fulfilment of honour and credibility, or the neutralisation of threats. While some conflicts are fought by informal, ad hoc groups, the majority of them involve state-controlled or orchestrated military forces.