War is a huge, destructive enterprise, wreaking havoc for decades and sometimes generations. It entails immense, sometimes irreparable national losses and can have global implications, such as disrupting trade or damaging the environment. It can destroy or damage the physical infrastructure that supports life, and impede access to education, medical services and food. It can also harm a country’s moral reputation and devastate families. Yet, despite the horrific toll that war can take on nations and peoples, there is little agreement about its causes or how to prevent it.

The vast majority of the theories that attempt to explain war’s causation fall into two broad categories. One group of theorists attributes it to innate biological or psychological factors or drives, with proponents including ethologists who draw analogies from animal behavior and psychologists and psychoanalysts.

Another set of theorists focuses on the institutions and international systems that states and their citizens inhabit, with proponents falling into two broad camps: liberals and socialists. These theories do converge in some respects, as both liberals and socialists tend to view states as the primary actors in war, but differ in their focus on how states are organized and regulated.

A third line of reasoning focuses on the nature and ethics of war. It draws upon philosophical teachings and insights, as well as the writings of such philosophers as St. Augustine and 17th-century Dutch thinker Benedictus de Spinoza. This school of thought emphasizes the importance of a proper code of conduct to avoid war, and it can include both liberals and socialists.

Finally, some theorists seek to explain war’s cause through cultural forces and institutions. They reject the determinism of biological and psychological explanations, but they still find it difficult to offer solutions for preventing war that don’t require cultural change.

In general, the more centralized power is in a country, the more likely it is to engage in war. Unchecked leaders are more prone to idiosyncratic ideologies and biases, and they may be more inclined to insulate themselves from critical information. This is why it is so important to reduce the concentration of power in all countries, from local city governments to the most powerful nation-states.

Of course, the five reasons for war are not mutually exclusive, and some scholars argue that each of them contributes to a particular kind of conflict. But, in order to understand why and how to end warfare, it’s essential to recognize that, on the whole, fighting is a last resort for most countries. As the costs of war are so high, they create powerful incentives for compromise and cooperation. In other words, the more costly a war is, the less likely both sides are to escalate and expand it. That’s why we need to keep it at bay, and that’s why we need the right incentives to promote a culture of peace. Like intensive care doctors who forget that human health is their natural state, analysts of warfare need to remind themselves of the incentives for peace.