Causes of War

Why wars rarely have just one cause

A cause of war is a factor that helps explain why a conflict begins. Across the development of warfare in Britain, recurring causes include disputes over political power, wealth, religion, national interests and ideology. Their importance changes with the circumstances of each period, and several usually work together.

It helps to distinguish a government’s reasons for wanting war from the conditions that make war possible. Wanting more territory creates a motive; building a larger army gives a government the means to pursue it. Equally, a dispute over money can become a dispute over political authority: who has the right to demand payment, and who can refuse?

The Crusades, the English Civil War, the Second World War and the Cold War show both continuity and change. All involved power and material interests, but the beliefs and ambitions used to justify conflict differed.

Religion and the medieval Crusades

The Crusades were a series of military campaigns from the late eleventh to the late thirteenth century. The medieval papacy promoted them with the aim of bringing the Holy Land, including Jerusalem, out of Muslim control and under Christian control. Religion therefore supplied a central purpose for warfare, rather than simply being a difference between the opposing sides.

In 1095, Pope Urban II addressed the Council of Clermont, urging Christians to take up arms to recover Jerusalem. His position as pope mattered: a religious leader was calling on Christians to fight for a religious objective. The crowd’s response, ‘Deus vult’ (‘God wills it’), expressed the belief that this was service to God. Knights were offered a holy vocation: they could see themselves as vassals, or servants, of God.

Religion also explains why individual Christians answered the call. Devout Christians wanted to make pilgrimages, religious journeys to holy places associated with Jesus. ‘Taking the cross’, or committing to crusade, was presented as a demonstration of Christian love and devotion. Crusaders were promised remission of sins, meaning forgiveness, and reduced time in purgatory, which Catholics believed was a state of purification after death before entry into Heaven. These spiritual rewards made participation matter for their hopes of salvation. Recovering and defending the holy places, and protecting Christians there, were also presented as acts of loving one’s neighbour. Crusaders could therefore regard fighting as a religious duty, despite the violence it involved.

Other motives reinforced this religious appeal. The papacy hoped crusading could help reunite the Catholic Western Church and the Greek Orthodox Eastern Church, linking religious leadership with political influence. Italian merchant states sought greater Mediterranean trade where Muslims controlled strategic seaports. Some nobles hoped to gain land in the Middle East: primogeniture, inheritance of the family’s land by the eldest legitimate son, left younger sons with fewer opportunities. Knights could also follow a crusading lord because of their feudal obligations.

Religion was therefore the leading cause because it supplied both the papacy’s central objective and powerful personal reasons to participate: devotion, pilgrimage and promised spiritual rewards. Trade, land and political influence helped explain support for the campaigns, but did not replace their religious purpose. These motives reinforced one another rather than operating separately.

Politics and the English Civil War

The English Civil War, 1642–1649, divided supporters of Charles I, known as Royalists or Cavaliers, from supporters of Parliament, known as Parliamentarians or Roundheads. At its heart was a struggle over how the country should be governed and how far the king’s authority should be limited by Parliament.

Relations between the monarchy and Parliament had already deteriorated under Charles’s father, James I. Charles also resented parliamentary interference. Meanwhile, wealthy and influential groups wanted a greater say in government. These competing expectations made compromise difficult.

How taxation and religion deepened the political dispute

Charles needed money to fund costly wars and royal expenditure. He demanded loans from wealthy subjects and sought increased customs duties. Parliament responded with the Petition of Right in 1628, which stated that the king should not impose taxation without Parliament’s consent or imprison people arbitrarily.

This was more than disagreement about the amount of money being collected. It raised a political question: could Charles use royal authority to obtain money without parliamentary approval? His other methods included knighthood fees, selling monopolies and extending Ship Money to inland towns. Each could increase resentment of government without Parliament.

Religion also weakened trust. Charles’s wife, Henrietta Maria, was a French Catholic. Some Protestants feared that the king or his children might convert to Catholicism and threaten England’s Protestant settlement. These were fears about what might happen, not proof that Charles had converted.

Charles’s appointment of William Laud as Archbishop of Canterbury added to these concerns. Laud’s changes to church services and worship appeared Catholic to Puritans, who wanted a more thoroughly Protestant Church. Religious opposition thus became connected to opposition to the king’s use of power.

From disagreement to a breakdown of trust

Charles dismissed Parliament and governed without it during his Personal Rule, also known by critics as the Eleven Years’ Tyranny. This avoided parliamentary challenges but did not remove his financial difficulties.

The need to fund an army against the Scots forced him to recall Parliament. When it refused to grant money, he dismissed it again. Military defeat then forced another recall: the Long Parliament assembled in 1640.

In 1641, the Puritan MP John Pym presented the Grand Remonstrance, a list of grievances against the king. Charles subsequently entered the House of Commons with an armed guard to attempt to arrest Pym and four other MPs. Trying to use force against parliamentary opponents deepened the loss of trust.

Politics provides the strongest connecting explanation for these disputes. Money and religion mattered greatly, but both repeatedly raised the same issue: whether Charles could govern as he wished or whether Parliament could restrain him.

Nationalism and expansionism before the Second World War

The Second World War began in 1939, following growing international tensions during the 1920s and 1930s. Nationalism is strong identification with a nation and support for its interests or unity. It could encourage demands for national unity and dominance. Expansionism is a policy of extending a state’s territory or control; it turned these ambitions into attempts to acquire territory.

Hitler wanted to unite German-speaking people in a Greater Germany and expand eastwards at the expense of the USSR, the Soviet Union. The first ambition concerned national unity; the second involved taking territory from other states. His aim of destroying communism also linked expansion with ideology.

These ambitions were not confined to Germany. Mussolini wanted a Fascist-Roman empire in the Mediterranean and East Africa. Japan sought a large empire in the Pacific, with ambitions extending towards China and Australia. These were imperial aims, not descriptions of everything those states successfully conquered.

Why ambitions became increasingly dangerous

Hitler’s rearmament challenged the Treaty of Versailles, which had restricted Germany’s military strength after the First World War. He expanded the army, navy and air force and greatly increased weapons production. Rearmament made an aggressive foreign policy more achievable: territorial ambition was backed by growing military power.

International responses failed to stop this aggression. Britain pursued appeasement, France was reluctant to intervene without British support, and the USA remained neutral. Hitler also believed that British and French opposition to communism might make them tolerate his actions in Eastern Europe.

The League of Nations failed to halt Japanese aggression in Manchuria, the Italian invasion of Abyssinia, and Hitler’s actions in Europe. These failures weakened the attempt to preserve peace through international cooperation.

Nationalism and expansionism supplied central motives for aggression. Rearmament supplied the means, while appeasement and the League’s failures reduced the obstacles. Explaining war therefore requires both the ambitions of aggressive states and the failure to contain them.

Ideology and the origins of the Cold War

An ideology is a system of beliefs about how society and government should be organised. After the Second World War, the capitalist USA and communist USSR became the leading powers in opposing groups of countries. Britain belonged to the Western group. The USSR dominated satellite states in Eastern Europe: countries that were formally separate but heavily subject to Soviet influence.

The Cold War was their prolonged political, economic, military and ideological rivalry, lasting from the aftermath of the Second World War to the collapse of communist rule in Europe around 1990. It was ‘cold’ because the USA and USSR did not fight a direct full-scale war against one another, not because the rivalry was peaceful.

The two powers had cooperated against Nazi Germany. Once that common enemy was defeated, their differences became central to decisions about Europe’s future.

Why capitalism and communism clashed

Capitalism is an economic system based on private ownership of businesses and property, with trade and production largely organised through markets for profit. Communism seeks common ownership and a classless society. In the Soviet system, the state controlled major property and production, claiming to act for the community.

Their contrasting principles help explain why each side opposed the spread of the other’s system:

These are principles and aims, not proof that either society achieved complete freedom or equality. The conflict concerned which system would shape post-war Europe. Ideological rivalry therefore became a struggle over political influence as well as economic organisation.

Rebuilding Europe became a struggle for influence

Germany made the disagreement especially clear. The USA wanted economic recovery and a return to democracy. American leaders feared that poverty and instability would encourage support for communism. Stalin, the Soviet leader, wanted heavy reparations to punish Germany. Their different plans made cooperation over reconstruction difficult.

Stalin also sought to dominate Eastern Europe and spread communist rule. Churchill described Europe’s division as an ‘Iron Curtain’ and called for resistance to Soviet expansion. This linked ideological disagreement to control over territory: the Western powers opposed the growth of Soviet influence, while Stalin strengthened his control over neighbouring states.

In 1947, the USA announced the Truman Doctrine, offering help to countries threatened by internal or external forces. Its purpose was containment: preventing communism from spreading further.

The Marshall Plan, proposed by US Secretary of State George C. Marshall, offered economic aid for post-war recovery. It supported containment by addressing the hardship that American leaders believed could strengthen communism. Stalin forbade Soviet satellite states from accepting this aid. Economic assistance thus became part of the rivalry, reinforcing the division between the two groups.

Germany and Berlin reveal the division

After the war, Germany was divided into four occupation zones administered by Britain, France, the USA and the USSR. Berlin was also divided between the four powers, even though the city lay inside the Soviet occupation zone.

In 1948, moves towards economic cooperation between the Western zones and the introduction of a new currency intensified disagreement. Stalin imposed a blockade of surface supply routes to West Berlin, attempting to force the Western powers to give way. The Western powers instead supplied the city by air. This Berlin Airlift allowed them to maintain their position, and the blockade was eventually lifted.

In 1949, Germany became two states: the Federal Republic of Germany, or West Germany, and the German Democratic Republic, or East Germany. Germany’s division showed how competing plans for recovery and government had hardened into opposing political systems. Berlin became a symbol of the wider Cold War.

Military rivalry reinforced ideological hostility

In 1949, the USSR tested its first atomic bomb, ending the USA’s monopoly of atomic weapons. Competition to build stronger nuclear forces became an arms race. This increased tension but also made direct war exceptionally dangerous: both powers risked devastating retaliation.

Military alliances strengthened the division. NATO, the North Atlantic Treaty Organisation, was formed by twelve Western powers in 1949 as a counterweight to Soviet military power. The USSR and its satellite states formed the Warsaw Pact in 1955.

Ideology was a central cause of the Cold War because it gave the powers incompatible visions of Europe’s future. However, ideological differences alone do not explain its development. Disputes over Germany, Soviet expansion, American containment, economic aid and military competition turned those differences into sustained conflict.

Have the causes remained the same?

There is continuity in the pursuit of power, land and wealth. Crusading nobles sought land, Charles I struggled over political authority, twentieth-century dictators pursued territorial dominance, and the Cold War powers competed for influence over Europe. Beliefs also repeatedly helped justify conflict: Christianity was central to the Crusades, while competing political ideologies shaped the Cold War.

Yet these similarities should not hide change. The Crusades centred on a papal call to recover holy places. The English Civil War centred on authority within a kingdom. Before the Second World War, national and imperial ambitions threatened the international order. During the Cold War, rival superpowers sought to defend and extend competing systems while nuclear weapons discouraged direct war between them.

A balanced judgement is that the broad categories of causes recur, but their relative importance, their particular expression and the way they combine change over time.