Our world can seem in constant conflict. Such struggles range from bullying and bitter Twitter debates all the way up to crime, terrorism, and war. War is, historically, one of the most impactful forms of conflict, shaping all our lives. Even if you haven’t been personally involved in war – whether through fighting or fleeing fighting – it has been involved with you. The social institutions of your country, for example, have been deeply determined by the wars of the past. This may have decided the very language you use to speak and think, and the population of people from which you’ve chosen your friends and loved ones. Many of today’s most prized pieces of technology – notably, the Internet and mobile phones – began as military inventions. Into the future, the realities of the Global War on Terror (GWOT), campaigns of cyber-harms, and the rivalrous schemes of such countries as America and Russia, as well as China, Iran, Israel, and Saudi Arabia (and let’s not forget all those armed non-state actors like al-Qaeda and ISIS) will configure some of the contours of our common life.

This book strives to widen and deepen reflection on three crucial questions about war: What is war? What should we do about it? And: How will war unfold in the future? In other words, this book aims to both describe and analyze war as a vitally important factual phenomenon, both now and into the future, as well as to evaluate war from a prescriptive or normative point of view. Ideally, this book aims to do so in a way both accessible and instructive for those with minimal education about armed conflict, yet will still stimulate worthwhile thinking, and rewarding questions, even amongst those with advanced background in the subject. The ambition is genuinely interdisciplinary, drawing heavily on facts and real-world cases, both historical and (mainly) contemporary, as well as such diverse theoretical resources as applied ethics, feminism, military strategy, philosophy, political science, and international law. The approach here is less one of arguing in favor of a particular theory or perspective and much more one of crafting an excellent, detached understanding of the pros and cons of the most important theories, and the most meaningful factual contexts which make the theories come alive.

Though the ontology of war is, inescapably, present throughout the whole book – “ontology” meaning the nature or reality of something – it will inform chapter 1 especially, and be rejoined at the end in chapter 7. It is pivotal to define and examine war in its manifold forms – e.g., civil versus international, symmetrical versus asymmetrical – alongside its various actors, and their means and ends of action, prior to a rewarding discussion of what we should do about it. There is not much point making judgments about, or recommendations for, something without knowing its form and nature, and how these evolve through time.

When we turn to such value judgments – in chapters 2–6 – we shall do so while drawing most heavily on what have been, and remain today, the three most foundational, detailed, influential, and richly suggestive theories. They are on a logical continuum, as shown in table I.1.

One such theory states that we should never go to war, especially when we know from history how devastating it is, how costly, brutal, and painful it is, and how frequently wars do not unfold the way one hopes or predicts. And there are compelling moral reasons, and abiding ethical principles, as to why we should not deliberately kill our fellow human beings, much less on the mass scale (and for “merely political” reasons) demanded by warfare. This, of course, would be the doctrine of pacifism, and it occupies what is arguably the optimistic and idealistic extreme in this regard: there’s always a superior option to war-fighting, and in terms of violent armed conflict, nothing is permissible and war should be outlawed and banned. A simple slogan of pacifism, in connection with war, might be: “Nothing goes!”

At the other extreme, the bleak and pessimistic one, would be realism. Realists tend to view all of human relations – or, at least, all of international relations – as governed by an endless power struggle. War is an entirely predictable consequence of this fact, as it’s one major method humans have to try to gain and hold power. There might not even be much we can do about it: there’s certainly no historical reason for thinking we can successfully ban warfare, or do away with it completely, as we all march together peacefully into a sun-lit future. To the extent to which we can do something about armed conflict, it should be to try to ensure that, when we get involved in warfare, we do so only because it’s manifestly in our self-interest (i.e., that it’s worth our while in terms of cost–benefit analysis) and, once we’re in it, we should be in it to win. So, anything conducive to the end of victory is fair game, and should be considered according to the same self-interested cost–benefit calculation as the original decision to go to war. Thus, the simple slogan capturing the essence of realism, in connection with war, might be: “Anything goes!”

To complete our basic logical continuum: if one option is to let anything happen in connection with war, and just leave it to the vicissitudes of perpetual power struggle; and if another option is to condemn all warfare absolutely, and assert that it’s never the proper thing to do, then of course that would leave a middle-ground option, according to which sometimes war might be both wise and even morally permissible, whereas other times it’s ill-considered and even unethical. This is the core proposition of just war theory or JWT (sometimes, war might be morally justified). It’s also an axiom of the so-called “laws of armed conflict” (LOAC) which have been agreed upon by most state governments around the world as one form of international law. Though the relationship between JWT and LOAC is not totally straightforward, as we’ll see and explore, it does make substantial sense to suggest they are close conceptual allies in this regard.

JWT/LOAC is thus the most complicated of the three basic doctrines or theories, as it takes quite a bit of time, effort, and complexity to specify which exactly are the times when war might be smart and just, and which other times it’s unwise or unjust. Realism and pacifism are more streamlined and straightforward, as they are more conceptually “pure” and one-sided in their attitude and understanding. This has the virtue of making them easier to understand and develop, and to see their forceful strengths, but may come at the cost of being more extreme and, in the end, harder to endorse overall. We will see that JWT/LOAC has substantial problems of its own. Alas, the perfect perspective on warfare may yet to have been invented. But such realities explain the breakdown of this book: after some good definitions and salient facts, we can orient ourselves quickly and powerfully by looking at the basic theories at either extreme of opinion. Realism thus gets chapter 2, and pacifism chapter 3. Then, we need more time and effort to explore the complex middle ground which, in a sense, attempts to split the difference. So, chapters 4–6 will analyze and critically evaluate JWT/LOAC, applying it fruitfully to many concrete cases.

We won’t ignore other theories – such as anthropology, Freudian psychology, “IR theory,” and the democratic peace thesis – and will draw upon them when the time is right. Moreover, we’ll pay considerable attention to the internal pluralism, and issues of division, within each of The Big Three theories. There are a number of such internal divides, and some of the most elemental are charted in Table I.1. In any event: the heart and soul of this book, when it comes to the issue of what to do about armed conflict and warfare, is to explore in rigorous, colorful, factually informed fashion, the powerfully stimulating and instructive debate between realism, pacifism, and JWT/LOAC, alongside the internal debate each tradition has regarding how best to view and apply its own core ideas and values. Out of such a spirited conceptual clash comes deeper theoretical understanding as well as a greater practical grasp of what we might do about the specter of constant conflict.