In January 1919, delegations representing thirty-two states began discussions in Paris on how to settle the enormous issues raised by the defeat of Germany, the collapse of the Austro-Hungarian, Russian, and Ottoman empires, and the spectre of left-wing revolution. In retrospect, they had little chance of constructing a lasting peace, because the way the recent conflict had ended made another great struggle almost inevitable. Allied troops remained outside German territory at the signing of the Armistice (although soon afterwards they occupied the Rhineland, Alsace, and Lorraine), while Germany remained the most powerful European nation in terms of both economic and political potential; yet the victors barred German delegates from participating in the peace discussions until after they had finalized non-negotiable terms. In Russia, messianic Marxists had seized power and repudiated all outstanding debts to former Allies, who refused to recognize their regime and excluded their delegates. In eastern Europe, finally, a plethora of weak states emerged to replace the great empires.

Although men had fought on foot throughout the Middle Ages, in the course of the thirteenth century infantry began to assume an increasingly significant role in Western warfare. The crossbow, albeit condemned by the Church, appeared in action with greater frequency, posing a considerable threat to the mounted warrior and his horse; the longbow, which could discharge arrows at the rate of about ten a minute (in contrast to the much slower rate of two bolts from the crossbow), could penetrate chain-mail armour with ease. The gradual introduction of plate armour from around 1250, to reinforce chain mail, reflects the recognized need to respond to the development of the bow, which would continue to influence the way war was fought for a century and a half.

The revolution in fortress design, the greater reliance on firepower in battle, and the increases in army size during the century 1530–1630 (see ) transformed the Western way of war. In particular, hostilities now affected more people (both directly, as the number of soldiers grew, and indirectly, as the impact of war on society augmented); and sieges far outnumbered battles. According to the experienced French soldier Blaise de Monluc, writing in the later sixteenth century, siegecraft constituted ‘the most difficult and the most important’ aspect of warfare, while in the words of Roger Boyle, earl of Orrery, a century later: ‘Battles do not now decide national quarrels, and expose countries to the pillage of the conquerors as formerly. For we make war more like foxes than like lions and you will have twenty sieges for one battle.’

Greek and Roman passages are cited by their manuscript numbers and can be easily identified by those citations in nearly all modern English translations.

From the reign of the emperor Diocletian (AD 285–305) until the development of firearms in the fourteenth century, the essentials of military organization, strategy, and tactics in Europe display a startling continuity. This reflects in part the enduring dominance of Roman military topography – the surviving infrastructure of fortified cities, fortresses, ports, and roads created in the third to fifth centuries. After the gradual dissolution of imperial power in the western half of the empire during the fifth century, those responsible for military decision-making in Rome's successor states had neither the inclination nor the resources to eliminate Roman walls. Like Byzantine emperors in the east, the Romano-German rulers differed little from the later Roman emperors in the means they used to control and make effective use of these assets. Continuity also reflects the unchallenged superiority of ancient military science, which decision-makers could find in books such as Vegetius’ Concerning Military Matters and the substantial contact between the West and Byzantium which stimulated the exchange and study of ancient military techniques.

Reference Guide to the Cambridge History of Warfare

Every culture develops its own way of war. Societies where land is plentiful but manpower is scarce tend to favour a ritualized conflict in which only a few warriors actually fight but their fate decides that of everyone. The ‘flower wars’ of the Aztecs and the ‘amok combats’ of the Indonesian islanders caused relatively little bloodshed because they aimed to seize people rather than territory, to increase each warlord's available manpower rather than waste it in bloody battles. With or without battles, however, as the Prussian officer and military theorist Carl von Clausewitz wrote in the 1820s, war is always ‘an act of force to compel the enemy to do our will’. Many non-Western military traditions have displayed great continuity over time. Even in the 1960s, anthropologists could study the highland peoples of Irian Jaya in Indonesia who still settled their disputes in the same ritualized way as their ancestors; but by then most other military cultures had been transformed by that of Europe and the former European colonies in the Americas. The Western way of war, which also boasts great antiquity, rests upon five principal foundations: technology, discipline, an aggressive military tradition, eclecticism, and finance.

Naval warfare in the West has been dominated for the past three centuries by large warships (‘capital ships’), using heavy artillery as their principal weapon, often drawn up in a single of line of battle so that their big guns could fire broadsides. The rival fleets of steel-clad steam-propelled warships at the battle of Jutland in 1916 deployed in much the same way as the rival fleets of wooden sailing warships in the battles of the Anglo-Dutch Wars, fought in much the same location, in the mid-seventeenth century.

In his remarkable study, The Sleepwalkers: How Europe Went to War in 1914, Christopher Clark noted the ‘unfortunate configuration of personalities’ in charge of Europe's destinies in 1914, and compared them with ‘a Harold Pinter play where the characters know each other very well and like each other very little’. The loquacious and indiscreet Kaiser visited his cousins, George V and Nicholas II, on several occasions, lionizing them in person and denigrating them in their absence. Franz Ferdinand circumnavigated the world in 1892–3, visiting Japan (just as Nicholas II would do a few years later), and a few months before his death he stayed with both George V and the Kaiser; but in private he was rude about them (and indeed about almost everyone else he met).

Incredibly enough, in the third century BC, Rome expanded simultaneously eastwards against the Greeks and Macedonians and west and south against Carthage, the great commercial and military power that had grown out of a Phoenician colony in present-day Tunisia. The three Punic wars (264–241 BC, for Sicily; 218–201 BC, for Italy and Spain; and 149–146 BC, for Carthage itself) were a struggle for the central Mediterranean which culminated in the abject destruction of Carthage. Throughout these conflicts, superior Roman military organization and infrastructure repeatedly demonstrated that the smallholders who made up the legions – as long as they fought in or near Italy – could overcome poor generalship and poor tactics, winning wars even when they lost major battles.

The speed of the Coalition forces’ victory in Operation ‘Desert Storm’ – less than four days of ground combat sufficed to drive the Iraqis into headlong retreat from Kuwait – seems to have taken the American administration by surprise: it had not yet decided when and how to terminate the war. On 27 February 1991 President George H. W. Bush, apparently without directly consulting his theatre commanders, declared that a ceasefire would take effect at midnight – allegedly because the ground war would by then have lasted exactly 100 hours. It proved a catastrophic decision for three reasons. First, contrary to early reports, Coalition forces had not yet sealed the border between Kuwait and Iraq, allowing many of Saddam Hussein's troops to escape; second, the elite Republican Guard units had largely extricated themselves and remained ready and able to protect the regime against domestic opposition; third, although Kuwait was now free, the war had done nothing to improve ‘the security and stability of the Persian Gulf’ – one of the president's stated war aims. In the armistice arranged shortly afterwards, the Americans handed their vanquished adversaries another priceless asset: the continued use of their helicopters. So when the Kurds in the north and the Shi‘a population of southern Iraq, trusting in earlier American promises of support, rebelled against Saddam Hussein, he easily crushed them, using chemical as well as conventional weapons to massacre tens of thousands – some of them before the eyes of outraged American troops.

When Ernst Jünger looked back on his experience as a young infantry lieutenant on the Western Front during the bloody summer of 1918, he combined the entries in his war diary with broader reflections. Not surprisingly, he contemplated the rise and fall of nations throughout history, a particularly pressing topic for him given that his beloved Germany stood at the precipice

Between 1763 and 1815 revolution and war changed the face and the heart of the Western world. When the Seven Years War ended in 1763, the British settlements along the Atlantic coast of North America were still colonies, dependent upon Britain. Across the sea in France, a monarchy that could trace its roots back more than eight hundred years ruled over a privileged aristocratic society, while serfs still worked the fields of their lords. The American and French Revolutions not only stand out as paramount events in the history of those two countries, but also went on to influence every corner of the Western world. The revolutionary tide that began in the United States eventually swept through Latin America as well. The transformation of French society that followed the fall of the Bastille to a Parisian crowd in 1789 changed not only France but Europe forever.

The end of World War II ushered in forty-five years of uneasy peace known as the ‘Cold War’. In the wreckage of the Axis collapse, two superpowers emerged to contest worldwide hegemony, their forms of government representing vastly different political and economic systems. In any other period, such differences and suspicions would have resulted in another great war; but over this contest hung the shadow of nuclear weapons whose destructive potential was such that in the end neither side dared resort to a direct military challenge to its opponent. After Hiroshima and Nagasaki, some predicted that nuclear deterrence would eliminate war and, in the sense that the United States and the Soviet Union never directly engaged each other in war, they were right. Hostilities still occurred, but for the most part they reflected the collapse of the colonial empires of the West in the aftermath of the world wars; and, while both the United States and the Soviet Union dabbled in these conflicts, they remained peripheral to the larger interests of the superpowers. In retrospect, one of the Cold War's great ironies was that it brought an unparalleled time of stability during which the contestants deterred each other from going over the brink.

In Robert Barret's military treatise of 1598, The Theory and Practice of Modern Wars, ‘a gentleman’ pointed out to ‘a captain’ that Englishmen in the past had performed wonders with longbows rather than firearms; to which the captain witheringly replied, ‘Sir, then was then, and now is now. The wars are much altered since the fiery weapons first came up.’ Most professional soldiers of the day agreed. According to Sir Roger Williams, another English veteran writing in 1590: ‘We must confess Alexander, Caesar, Scipio and Hannibal, to be the worthiest and most famous warriors that ever were; notwithstanding, assure yourself … they would never have … conquered countries so easily, had they been fortified as Germany, France, and the Low Countries, with others, have been since their days.’

After victory over Spain in 1659, France became the pre-eminent land power in Europe and transformed the face of Mars. The Bourbons expanded wartime forces, improved military administration, and created a powerful standing army, and in doing so set a new pattern for Europe. Prussia and Russia imported this design and found that it required governmental as well as military reform. Through warfare, these two new powers carved out a place beside the other European states. At sea the British dominated, shouldering aside the Spanish, Dutch, and French to expand British colonial holdings. Finally, Western powers put warfare on a truly global stage in the Seven Years War, as they contested dominion in Europe, the Americas, and India. The period from 1661 to 1763 provided a historical theatre for the ambitions of powerful statesmen who both refashioned their military instruments and wielded them in a series of wars for glory and empire.