I first wrote on this subject some years ago for an encyclopaedia examining war and religion. I have revisited and expanded the piece here for a wider audience, while retaining its central concern: the relationship between religious conviction, political authority and the use of force.

When religion and politics meet, questions of power are never far away. This is particularly true when political communities contemplate the use of military force.

Political theology is concerned broadly with the relationship between our understanding of God and the way human societies organise and exercise political power. William Cavanaugh and Peter Scott describe it as the analysis and criticism of political arrangements from the perspective of different understandings of God’s relationship with the world. Put more simply, political theology asks what our deepest convictions about God, humanity and the good life mean for the way societies should be governed. War brings that question into particularly sharp focus.

If we understand war, following Clausewitz, as armed conflict pursued for political purposes, then decisions about war inevitably involve judgements about political authority, justice, responsibility and the value of human life. Where religious conviction shapes those judgements, theology and politics intersect.

That intersection is hardly new. War and religion are as old as human society itself. The attempt to separate religion neatly from politics is, historically speaking, a relatively modern development. Such a distinction would have made little sense in the political worlds of ancient Athens or Sparta, or in much of medieval and early-modern Europe. Political authority and religious belief were frequently intertwined.

In a theocratic society, where political authority is understood ultimately to derive from God, a decision to wage war cannot easily be separated from the perceived will of the deity. Christianity encountered this problem particularly acutely following the conversion of the Emperor Constantine. A faith that had developed largely outside the structures of imperial power now had to consider its relationship with political authority.

The Apostle Paul’s statement that there is no authority except that which God has established raised difficult practical questions. What did obedience to political authority actually require? What happened when rulers acted unjustly? Could Christians legitimately exercise political power? And could participation in war ever be compatible with Christian faith? These were not merely abstract theological questions. They concerned the realities of government, violence, justice and responsibility.

Augustine and the two cities

Few thinkers have influenced subsequent Christian reflection on these questions more than Augustine. His City of God was written partly in response to claims that Rome’s adoption of Christianity had contributed to the decline of the Empire. Augustine’s answer was much more profound than a defence of Christianity against its critics. He sought to place political life itself within a larger understanding of human history. The Roman Empire was neither eternal nor ultimate.

Augustine described human existence in terms of two cities: the City of God and the earthly city. These are not simply two political territories existing alongside one another. They represent different loves, loyalties and understandings of human purpose, yet they remain intimately intertwined within history. This gives Augustine’s political thought a particular realism. Political institutions matter. Justice matters. Peace matters. Yet no political order can finally become the Kingdom of God.

War therefore occupies an uncomfortable but important place within his thinking. Augustine did not regard war as intrinsically good; peace remained the desired condition. Nevertheless, he believed that under certain circumstances participation in war could be morally permissible. Political responsibility could require the use of force to restrain wrongdoing and restore a just peace. That tension has remained within Christian political thought ever since.

Can the pursuit of peace sometimes require the use of force? Can love of neighbour include protecting the innocent from aggression? And who has the authority to decide when such action is justified? Later Christian just-war thinking would develop much more detailed answers, but Augustine helped establish the intellectual framework within which those questions could be asked.

Can faith really be private? The relationship between Christianity and war remains deeply contested, as indeed it does within other major religious traditions. One particular difficulty emerges from the modern liberal distinction between the public and the private. Religion is frequently understood as belonging primarily to the private sphere: something concerned with individual belief, worship and personal morality. Politics, by contrast, belongs to the public sphere.

That distinction can appear attractive in religiously plural societies. It offers a way of allowing people with very different beliefs to live together without one religious tradition controlling the state. But the distinction is more difficult to sustain than it initially appears. Our convictions about justice, human dignity, freedom, responsibility and the value of human life do not suddenly disappear when we enter the public square. Religious believers inevitably bring some understanding of the world with them when they make political and moral judgements. So, of course, do those who hold no religious belief.

The important question may therefore be less whether religion should influence politics than how people with different fundamental convictions reason together about questions of common concern.

Three thinkers illustrate very different ways of approaching that problem.

Reinhold Niebuhr: the realism of power

Reinhold Niebuhr became one of the most influential American Protestant theologians and political thinkers of the twentieth century. He is particularly associated with what became known as Christian Realism. Central to Niebuhr’s thinking was a sober understanding of human nature.

Individuals may be capable of considerable generosity and self-restraint, but groups, institutions and nations frequently behave differently. Collective interests can magnify pride, fear and the desire for power. Nations therefore tend to pursue their own interests and can seek dominance over others.

Niebuhr had not always reached that conclusion. After the First World War he embraced pacifism and became a strong critic of capitalism. But the political developments of the 1930s, particularly the rise of Hitler, profoundly affected his thinking. He became an increasingly forceful critic of pacifism. The tension for Niebuhr lay partly between love and justice.

Love represents a demanding moral ideal. Justice, however, operates in a world in which rights sometimes have to be protected and wrongdoing restrained. Where power is being used oppressively, moral aspiration alone may be insufficient. Power may have to be challenged by power. For Niebuhr, therefore, the Christian cannot simply retreat from political responsibility because the choices available are morally imperfect. Sometimes responsibility involves acting in circumstances where every available option carries moral cost. His realism refuses the comforting assumption that good intentions are sufficient.

Stanley Hauerwas: the alternative community

Stanley Hauerwas approaches the relationship between Christianity and political power very differently. Where Niebuhr came to reject pacifism, Hauerwas became one of the most prominent modern advocates of Christian nonviolence, influenced significantly by the work of John Howard Yoder. Hauerwas’ argument is connected to a much broader criticism of liberalism.

The liberal political tradition associated with thinkers such as Thomas Hobbes and John Locke places considerable emphasis on the autonomy of the individual. Hauerwas argues that this can encourage us to imagine society primarily in terms of individuals pursuing their own interests while political institutions provide the mechanisms through which those interests are negotiated. For Hauerwas, Christianity offers a fundamentally different account of human community.

The task of the Church is therefore not simply to support the liberal state or provide it with religious legitimacy. The Church should itself embody a different kind of political community: an alternative polity demonstrating what human relationships can look like when they are shaped by faithfulness, trust and peace rather than fear and coercion.

The contrast with Niebuhr is significant. Niebuhr asks how Christians can exercise responsibility within the realities of political power. Hauerwas asks whether accepting those realities too readily risks allowing the state to define the limits of Christian moral imagination. One emphasises responsible engagement with an imperfect world; the other challenges Christians to ask whether their willingness to use political power has compromised the distinctiveness of their witness. The tension between them is not easily resolved.

Habermas and the secular public square

Jürgen Habermas approaches these issues from a very different intellectual tradition. A German philosopher associated with critical social theory, Habermas has spent much of his academic life exploring rationality, communication, democracy and the conditions necessary for meaningful public discourse.

His work on the public sphere and communicative action asks how citizens who hold very different beliefs can nevertheless reason together about matters that affect their common life. His attitude towards religion developed considerably.

From an intellectual background strongly influenced by Marxist criticism of religion, Habermas later came to recognise that modern secular societies cannot simply treat religious belief as an obsolete remnant of the past. His public dialogue with Cardinal Joseph Ratzinger, who later became Pope Benedict XVI, demonstrated his increasing recognition of the extent to which Western political and moral thought has been shaped by its Christian inheritance.

Religion, for Habermas, cannot simply be circumvented. Religious traditions continue to contain moral ideas, language and insights capable of contributing to public reasoning. The challenge is therefore to establish meaningful dialogue between religious and secular ways of understanding the world.

This does not mean that religious claims should automatically determine public policy. Nor does it mean that secular citizens must accept theological premises they do not share. It means that neither side can simply declare the other intellectually illegitimate before the conversation begins. That is an important insight for a plural democratic society. Religion, politics and the responsibility to reason

Niebuhr, Hauerwas and Habermas arrive at very different conclusions, but each exposes the difficulty of pretending that religion and politics inhabit entirely separate worlds. Niebuhr confronts us with the realities of power and the possibility that political responsibility may sometimes require morally difficult action. Hauerwas asks whether Christians become too comfortable with those realities and whether the Church’s first responsibility is to embody an alternative way of living. Habermas, approaching the question from outside Christian theology, recognises that religious traditions continue to contain moral resources that secular societies cannot simply dismiss.

Behind all three lies a deeper question.

Can our most fundamental convictions ever really be private? The distinction between public reason and private belief undoubtedly has value. No modern plural society could function if every religious group simply demanded that its theological convictions become law. But neither can citizens divide themselves neatly in two.

Our understanding of what a human being is, what justice requires, what makes authority legitimate, when force becomes oppression and what obligations we owe to strangers inevitably shapes our political judgement. For some, those convictions will have religious foundations. For others, they will arise from philosophical, political or secular traditions.

The task of a healthy public sphere is not to pretend that these differences do not exist. It is to create the conditions in which they can be examined, challenged and discussed with intellectual seriousness. War makes that task particularly urgent.

A decision to go to war is among the gravest decisions any political community can make. It places human beings in circumstances where they may intentionally take life, risk their own lives and expose others to suffering. Questions about political authority, moral responsibility, justice and the proper limits of power therefore become unavoidable.

Political theology does not provide simple answers to those questions. What it does is remind us that decisions about war do not emerge from a moral vacuum. They arise from deeper understandings of human nature, justice, authority and the kind of world we believe we inhabit.

And perhaps that is why the relationship between religion and politics remains so difficult to resolve. We are not merely debating policies. We are debating the convictions from which our understanding of the world begins.