What can history’s great armies teach us about the bond between a nation and its military? In a recent podcast we explored this question with Sir Barney White-Spunner, whose new book Nations in Arms: Five Armies That Made Europe examines how five pivotal armies not only won battles but also transformed the societies they served. It’s an “incredibly timely” study, as today’s world reminds us that war can re-emerge even after decades of peace. White-Spunner argues that governments must “fundamentally re-think their relationship with armies and soldiers” in light of modern threats.

By looking at five case studies – from ancient Rome to World War II America – we see a recurring theme: armies are shaped by the values and needs of their societies, and in turn, they become powerful agents of social change. This article blends insights from the book and podcast with deeper historical research to paint the broader picture of each army’s legacy. It’s written for enthusiasts rather than experts, aiming for an academic tone that remains accessible and engaging. Let’s delve into each of these five armies, exploring how they were organized, what they stood for, and how they changed the course of history and society.

Constantine’s Roman Army – Refounding an Empire

In the early 4th century, Emperor Constantine the Great rebuilt the Roman Army – and in doing so, refounded the Roman state. Constantine rose to power amidst chaos; civil wars and barbarian invasions had shaken Rome. To restore stability, he reformed the army’s structure and its relationship to the imperial government. He separated civil and military authority, ending the old system where provincial governors doubled as generals. This prevented regional powerbases and ensured the army’s loyalty was to the Emperor alone. Constantine also expanded the mobile field armies (comitatenses) while maintaining frontier garrisons (limitanei), creating a more flexible defense in depth. Crucially, he introduced the gold solidus coin to stabilize the economy and guarantee soldiers’ pay. By securing the army’s loyalty through reliable pay and reform, Constantine set the stage for a stronger central state.

Perhaps the most enduring change was the army’s “soul” – its religious character. Constantine was the first Roman emperor to convert to Christianity, especially after his victory at the Battle of Milvian Bridge in AD 312 which he attributed to Christian divine aid He decriminalized Christianity and eventually made it an officially favored religion This was a turning point in the Roman Army’s identity. Earlier, soldiers had worshipped Jupiter or Mars; now they fought under the banner of the Christian cross. The famous story goes that Constantine’s troops painted the ☧ (Chi-Rho) symbol on their shields after he received a prophetic vision, rallying them with a new spiritual unity. By elevating Christian faith within the army, Constantine’s reforms not only saved the empire from anarchy – they also Christianized Europe’s foremost institution of power. In the long run, this paved the way for the Christian Byzantine Empire and the medieval European order.

Constantine’s army reforms had other social impacts as well. To ensure a stable supply of recruits and resources, he tied certain professions to hereditary duty – for example, sons of soldiers had to become soldiers, farmers were bound to their land to secure grain supply, etc. This laid foundations for the more rigid social structure of the Middle Ages (foreshadowing serfdom and guilds). In short, Constantine reshaped the army to be more disciplined, mobile, and ideologically unified, and in turn that army reshaped Roman society. It safeguarded the empire’s frontiers for decades, and its embrace of Christianity steered the spiritual future of Europe. No wonder historians consider Constantine’s reign a distinct epoch transitioning Rome from classical antiquity to the Middle Ages. In White-Spunner’s terms, Constantine’s example shows how a visionary leader can adapt an army successfully – strengthening its loyalty, its organisation, and even its “soul”, with effects lasting centuries.

Mehmet the Conqueror’s Ottoman Army – Cohesion and Conquest

In the spring of 1453, Sultan Mehmet II’s Ottoman army stood before the mighty walls of Constantinople. What followed was a military triumph that “sealed the Ottomans’ status as a formidable power”, ending the Byzantine Empire and shaking the world. But this victory was not just about big cannons and large numbers (though the Ottomans had plenty of both). It was the product of a unique military system deeply rooted in Ottoman society – a system that gave the army extraordinary cohesion and made it an agent of imperial transformation.

Figure: “Mehmet II conquering Constantinople” (painting by Fausto Zonaro, 1903). In 1453 Sultan Mehmed’s elite Janissaries and other Ottoman forces breached the walls of Constantinople, ending the Byzantine Empire. This victory exemplified the Ottomans’ advanced use of gunpowder artillery and the iron discipline of the Janissary corps, which formed the Sultan’s loyal standing army. Their success not only expanded the empire’s territory but also transformed the city into Istanbul – the new imperial capital of a Muslim-majority empire.

At the core of Mehmet II’s army were the Janissaries, often called the first modern standing infantry army. Uniquely, Janissaries were created via the devşirme, a “child levy” that took Christian boys from the Balkans, converted them to Islam, and trained them rigorously as the Sultan’s household troops. This practice meant the army was literally forged from the empire’s subject populations. Shaped by society: the multi-ethnic, multi-religious nature of the Ottoman realm produced a corps of soldiers with no loyalties except to the Sultan. Janissaries were forbidden to marry or trade until age 40, reinforcing their singular devotion They were paid a regular salary (unlike feudal levies), making soldiering a respected lifelong profession. This strict discipline and isolation gave the Ottoman army an internal cohesion rarely seen in medieval forces. Contemporary observers were astonished by the Janissaries’ drill and willingness to face gunfire – indeed, they were among the first infantries to widely use firearms, giving the Ottomans a technological edge.

When Mehmet II besieged Constantinople, he not only deployed this elite infantry but also huge cannons (including the famous “Orban’s” bombard) and a massive force, possibly 80,000–100,000 strong. The result was a foregone conclusion: after a 53-day siege, the city fell. The conquest of Constantinople in 1453 was more than a military victory; it was a civilizational shift. Mehmet II transformed the ancient Christian city into Istanbul, a flourishing capital of the Ottoman-Islamic world. He resettled populations into the city and patronized arts and architecture, jump-starting its revival as a “thriving imperial capital” by the end of his reign. The army had made this possible – without the disciplined Janissaries and innovative artillery, the Ottomans might never have taken the city’s impregnable walls.

The Ottoman army’s success also transformed Ottoman society. The Janissaries became a powerful political class in the empire. Originally slaves of the state, over time they gained privileges: by the 17th century, the recruitment rules relaxed and even Muslim families got their sons into the corps to elevate their social status. In effect, the Janissary corps “civilianized” and became an entrenched interest group within society. They frequently intervened in politics, at times marching to depose sultans who threatened their perks. This dynamic shows the feedback loop between army and society: the empire’s inclusive approach created an unbeatable army, and that army in turn wielded huge influence over the empire’s governance and stability. Eventually, the Janissaries’ conservatism – resisting any military modernization – contributed to Ottoman decline, until a later Sultan forcibly abolished the corps in 1826. But during Mehmet II’s era, they were still a progressive force, driving the Ottomans’ rapid expansion. White-Spunner includes the Ottoman army of 1453 as a case study in successful adaptation: it had loyalty, organization, and soul, to use his terms. Its loyalty was ruthlessly to the Sultan, its organization was cutting-edge for its time, and its soul was a zealous belief in the empire’s destiny (bolstered by religion and the promise of plunder and privilege). In sum, Mehmet’s army was shaped by the Ottoman societal mosaic, and it, in turn, transformed the map of Europe and Asia – ushering in a new age.

Cromwell’s New Model Army – Revolutionizing War and Politics

In the midst of the English Civil War, Oliver Cromwell and Parliament created the New Model Army in 1645, and nothing like it had been seen before in England. It wasn’t just a military unit; it was, as one historian calls it, “a political entity in its own right” that carried “radical political ideas and dissenting religious beliefs” within its ranksthe-past.com. Shaped by its society’s turmoil, this army of zealous Protestants and commoners broke the mold of aristocratic command. And it ended up transforming society by helping overthrow the monarchy, executing a king, and briefly turning England into a republic. The New Model Army exemplifies how a military force can be an engine of revolution.

Prior to 1645, Parliament’s forces in the civil war were led by various regional lords with their own troops. Cromwell and Sir Thomas Fairfax pushed for a centralized, professional army open to talent rather than birth – the result was the New Model Army, a standing force of about 22,000 men paid by the state and promoted on merit. For example, many officers were self-made men of Puritan faith, not nobles. Discipline was strict, and religious zeal was the key to victory, as Cromwell believed. Soldiers received preaching and carried pocket Bibles; this gave them a unifying “godly” cause. In battle, their morale and cohesion proved decisive. The New Model Army crushed the Royalists at Naseby (1645), a victory often credited to its well-drilled infantry and aggressive Ironsides cavalry (which Cromwell himself led)t This triumph marked “the decisive turning point in the English Civil War”, effectively sealing King Charles I’s defeat.

Yet the importance of the New Model Army went beyond military victory. It had a profound political and social impact off the battlefield. In 1647, after the war, the Army found itself at odds with the Parliament it had served. The common soldiers – many influenced by radical groups like the Levellers – demanded political reforms, religious freedom, and back pay. They even convened debates (the famous Putney Debates of 1647) to discuss a new constitution and expanded suffrage. The Army occupied London multiple times to pressure the civilian government. Ultimately, it was army officers and troops who decided King Charles I must be brought to trial when Parliament faltered. In 1649, the New Model Army’s leaders purged Parliament (Pride’s Purge) and set up the court that executed King Charles I, an unprecedented act of regicide. As historian David Flintham notes, 1647 was a year the Army “took centre-stage in English politics, heralding a seismic shift in attitudes towards the King”, leading directly to his execution.

For a decade, England became a Commonwealth (republic), with Oliver Cromwell eventually ruling as Lord Protector – all backed by the Army’s muscle. The Army enforced Puritan moral policies and fought wars in Ireland and Scotland to secure the new regime. It was so influential that some contemporaries feared England had gotten a “sword-governed” military rule. Indeed, the Army was the social agent of revolution: it had elevated Cromwell (its general) to power, and it later even removed Cromwell’s son from succession, effectively ending the Protectorate when the Army’s confidence waned. Paradoxically, the same Army that built the republic also facilitated the Restoration of the Monarchy in 1660 – generals from the New Model Army played a role in negotiating King Charles II’s return once they lost unity after Cromwell’s death. This underscores that the Army had its own corporate interests and identity separate from any single faction.

Why was the New Model Army so socially transformative? Firstly, its internal culture was unusually egalitarian for the 17th century. Common soldiers, often literate artisans or farmers, felt empowered to voice political opinions. Many held “dissenting or radical views unique among English armies”, as the Army’s religious independence fostered free thinking. Senior officers like Cromwell did not share all these radical democratic ideas, but they tolerated debate to an extent. Secondly, the Army’s very existence – a large standing army – was novel in England. It created financial strain and forced new taxes, stirring public debate on liberty versus security. Thirdly, the Army became a model (as its name suggests) for future military organization: a national, professional force rather than a feudal levy or mercenary band. Although the New Model Army was disbanded at the Restoration (except for a few regiments), the English distrust of standing armies persisted for centuries as a result of this period, shaping Britain’s civil-military relations (Parliament kept the army under tight control henceforth).

In White-Spunner’s framework, the New Model Army illustrates an army that dramatically reshaped its nation’s politics. It had a clear ethos – devout Protestantism and republican sentiment – giving it a distinct “soul.” Its loyalty was controversial: nominally to Parliament, but in practice often to its own leadership and principles. Its organization (centralized, meritocratic, disciplined) made it formidable in war and influential in peace. Enthusiasts of military history often call it “the most influential army in English history” for good reason. The New Model Army shows how a military born from societal upheaval can in turn become the midwife of a new social order – albeit one that proved temporary in this case.

Prussia’s Army of the Napoleonic Wars – The Nation in Arms

Perhaps no example better embodies the idea of a “nation in arms” than the Prussian Army of 1806–1815. In 1806, Prussia’s old-fashioned army was humiliatingly crushed by Napoleon at Jena-Auerstedt, a national trauma that exposed how out of touch the military was with modern warfare and with its own societyen.. In response, a group of reformers led by Generals Gerhard von Scharnhorst and August von Gneisenau set about modernizing not just the army’s tactics and organization, but its very relationship to the Prussian peopleen.. The result by 1813 was an army that, for the first time, drew on the patriotic zeal of the middle class and commoners, not just the obedience of conscripted peasants or hired mercenariesen. This reformed Prussian Army helped defeat Napoleon in the Wars of Liberation – and in the process, it transformed Prussia into a modern nation-state.

The Prussian military reformers recognized that France had unleashed something new: the levée en masse – whole nations mobilized for war. Prussia, still stuck in 18th-century habits, had an army of limited size, comprised mostly of peasant conscripts serving long terms and officered solely by nobles. After the 1806 disaster, Scharnhorst’s committee introduced sweeping changes: merit-based promotion and open recruitment. In 1807–08, they “reopened the officer corps to the middle class” and made education and talent the basis for advancement, threatening the old aristocratic monopoly. They founded a War Academy in Berlin to train competent officers, including bourgeois candidatesen.. Scharnhorst also shortened military service and implemented the Krümpersystem, a rotation that trained far more men than allowed by the standing army limits – creating a large reserve of citizens with military training.. In effect, Prussia moved toward universal military service, a radical idea for its time. By 1813, this led to the creation of the Landwehr, a militia of middle-class volunteers that supplemented the army, and indeed thousands of patriotic volunteers flocked to the colors when war with France resumeden.wikipedia.org.

These reforms were explicitly aimed at harnessing patriotism. The reformers were “dismayed by the populace’s indifferent reaction to the 1806 defeats” and sought to “cultivate patriotism within the country.” To that end, they abolished serfdom in 1807 (a social reform led by Baron vom Stein) so that citizens could feel invested in the state. Citizenship, duty, and armed service became entwined. King Frederick William III, though cautious, eventually endorsed many changes – even introducing the Iron Cross decoration in 1813, which notably could be awarded to common soldiers for valor (a break from aristocratic orders of chivalry). By the time Prussia rose against Napoleon in 1813, the difference was stark: “In comparison to 1806, the Prussian populace, especially the middle class, was supportive of the war, and thousands of volunteers joined the army.” The citizen-soldier ideal had arrived. Prussian troops, fighting with newfound national fervor, played a vital role in victories like the Battle of Leipzig (1813) and Waterloo (1815), as Blücher’s Prussian corps became indispensable allies to Britain and Russia.

The social transformation wrought by this “nation in arms” was significant. “The officer corps was reopened to the middle class… advancement into higher ranks became based on education.‘ That meant the army was no longer purely a Junker (noble) preserve; the military became a channel for social mobility and national integration (albeit slowly – full equality took more time and some reforms backslid after 1815). The very concept of military service as a duty of citizenship took root in Prussia and later in unified Germany. This had lasting effects: a broadly trained male populace, a reserve system, and a strong martial tradition in society. However, the reformers also encountered conservative resistance. Some traditionalists feared that arming the middle class and granting them leadership would “promote the ideas of the French Revolution” and erode aristocratic privileges. Indeed, after Napoleon’s defeat, the Prussian court pulled back on the most liberal aspects – the army remained a pillar of the conservative order (and by the mid-19th century, Prussia’s army was again used to suppress revolutions). Nonetheless, the genie of national fervor was out of the bottle. The Prussian experience demonstrated that a state fighting for its very survival could successfully turn its army into a true “army of the people.” White-Spunner highlights this as a case of an army adapting in both battlefield effectiveness and in “how they relate to the state which it is their duty to protect”. The lessons from Scharnhorst’s reforms – about training, merit, citizen enlistment, and civil-military synergy – were influential across Europe.

It’s worth noting the ideological side: figures like Clausewitz (who served on the reform committee) articulated that war is “a trinity” of government, army, and people – an idea born from these Napoleonic experiences. Prussia’s 1813 “War of Liberation” against French occupation became a founding myth of German nationalism. The notion of a citizen army with a patriotic “soul” took hold, arguably planting seeds for both the unification of Germany later in the 19th century and the intense militarization (for good and ill) of German society thereafter. In short, the Prussian Army’s transformation showed how a backwards army could reinvent itself by aligning with societal change – freeing the serfs, empowering the middle class – and in turn, that army forged a new national identity that outlasted the wars.

The U.S. Army in World War II – A Citizen Army & Social Catalyst

In 1941, the United States had a relatively small, volunteer army – about 190,000 soldiers – ranking behind many world powers Four years later, over 8 million Americans wore the U.S. Army uniform, part of a total 16 million Americans in all services, mobilized to fight in World War II. This dramatic expansion created what was truly a citizen army: millions of draftees from every walk of life, training and serving alongside volunteers. The U.S. Army of World War II not only defeated the Axis abroad; it also became a powerful agent of social change at home. It helped pull America out of the Great Depression, accelerated social integration (albeit incompletely), and reshaped post-war society through programs like the G.I. Bill. In White-Spunner’s terms, the U.S. Army of 1941–45 brilliantly “adapted successfully” to meet a vast challenge, and its legacy continues to offer lessons on the military-society relationship.

America’s involvement in WWII required total mobilization of society. After Pearl Harbor, the U.S. implemented the Selective Service draft on an unprecedented scale. By war’s end, over 10 million men had been conscripted, in addition to volunteers – truly a “nation in arms”. For the first time, the U.S. government consciously shaped the Army to mirror the nation. Draftees were a cross-section of American society (with some exceptions due to segregation and gender). The Army expanded specialized training programs and stood up new branches (e.g., the Army Air Forces) to effectively use America’s industrial and technological might. Women also entered military service in non-combat roles through the WAC (Women’s Army Corps) and other units, marking a significant shift in personnel policy. Over 150,000 women served in the Army during WWII – a societal breakthrough, although in segregated units and often facing skepticism. Likewise, African-Americans served in large numbers (over 1 million in uniform), though in segregated units; the war effort prompted critical examination of these practices, laying groundwork for integration a few years later (President Truman desegregated the armed forces in 1948). Thus, the WWII Army was both shaped by existing social norms (it mirrored racial segregation and gender roles of the time) and it became a catalyst for change, as the pressures of total war made it harder to justify those inequities.

Figure: U.S. war poster (1941–45) – The United States framed World War II as an all-encompassing national effort. Posters like “Follow Me! Men of 18–19, these can be yours – apply now at any U.S. Army recruiting station” urged young Americans to enlist. Such recruitment and propaganda campaigns reflected the ideal of the citizen-soldier, and by 1945 the U.S. Army swelled to over 8 million personnel through conscription. This mass mobilization not only helped win the war but also spurred profound social changes at home (the wartime experience broadened horizons for many and led to benefits like the GI Bill).

On the home front, the Army’s needs drove massive industrial and economic mobilization. Unemployment virtually disappeared as factories converted to produce tanks, planes, and weapons (“Mobilizing a nation for war” meant women like “Rosie the Riveter” joined the workforce, and migration patterns changed as people moved to industrial centers). The Army in the field was also a melting pot: rural farm boys served alongside urban dwellers, second-generation immigrants alongside old stock Yankees, forging a shared experience. Supreme Commander Dwight Eisenhower later remarked on how this military service bound Americans together and gave them a broader perspective beyond their hometowns.

The war ended in total victory, and the citizen-soldiers came home. Here, the U.S. did something arguably as important as winning the war: reintegrated millions of veterans and rewarded their service with opportunities, rather than neglecting them (as had happened after World War I). The Servicemen’s Readjustment Act of 1944, better known as the G.I. Bill of Rights, was a landmark policy that treated the returning Army as an asset to society. It provided funding for education, low-cost home loans, and unemployment support for veterans. The effects were dramatic: By 1947, veterans made up nearly half of college admissions, and by 1950, the number of college graduates had surged, vastly expanding the educated middle class. Millions of veterans became the first in their families to own homes, thanks to G.I. Bill loans – fueling a post-war housing boom and the growth of suburbs. In short, the U.S. Army in WWII was a social leveler and accelerator: it took in young men from disparate backgrounds, gave many technical training or leadership experience, and then, via veteran benefits, turned them into doctors, engineers, homeowners, and entrepreneurs. Historians often credit the G.I. Bill as one of the greatest social legislations in American history, transforming American society by creating opportunity for the Greatest Generation.

Of course, not all changes were rosy or fully equitable – racial minorities did not benefit equally at first (many Black veterans in the segregated South faced barriers using their G.I. benefits, for example). Women who had made gains in employment were often pressured back to domestic roles after 1945. Yet, the war sowed seeds for the civil rights and women’s rights movements by exposing hypocrisies and expanding horizons. The U.S. Army itself was permanently changed: post-WWII, the U.S. abandoned its traditional small peacetime army stance and maintained a large standing military into the Cold War. The American public’s relationship with its Army also shifted – the citizen-soldier ideal remained a point of pride, but the experience of large-scale mobilization also meant the society would henceforth question and challenge the use of its military (seen later in Vietnam War dissent, etc.). In White-Spunner’s analysis, the American Army of 1941–45 demonstrated how a democratic society can rapidly gear up an army that reflects its values (individual initiative, technological ingenuity, and eventually, pluralism) and how that army can “offer solutions” for modern challenges – indeed, many of today’s military innovations in organization and veterans’ welfare trace back to lessons learned in WWII.

Conclusion: Armies and Societies – A Two-Way Street

From Constantine’s legions to World War II G.I.s, these five case studies confirm a powerful insight: armies are not isolated from their societies, but products of them – and drivers of change within them. Each of these “nations in arms” arose at a pivotal historical moment when old ways of war had to change, and in changing how they fought, they changed who they were.

What common principles emerge? One is the importance of loyalty and legitimacy. Constantine’s Christianized army bound soldiers’ loyalty to a unifying faith and emperor; Mehmet’s Janissaries had singular loyalty to the Sultan; Cromwell’s New Model Army was driven by ideological loyalty to a cause; Prussia’s reformed army fostered patriotic loyalty to the Fatherland; and America’s citizen army fought for a vision of democratic freedom. In each case, the army had a clear sense of purpose or “soul” that resonated with a broader segment of societyospreypublishing.com. This gave them staying power in crises.

Another principle is organization and adaptability. Successful armies rethought their structures – whether it was Constantine separating military commands, the Ottomans integrating new technology and standing troops, Cromwell instituting merit promotions and drill, Prussia embracing conscription and staff training, or the U.S. revolutionizing training and logistics for global war. These changes often required overcoming internal resistance (e.g. Prussian nobles, Janissary elites, etc.), meaning society had to accept reforms too. Thus, military reform and social reform often went hand in hand.

Finally, these cases show that when an army becomes a true mirror of its society (or a broad section of it), it can unlock tremendous energy. But it can also pose challenges: a politicized army like the New Model could challenge civilian rule; a militarized society like Prussia’s carried the risk of hawkishness. The key is balance and clarity of purpose. White-Spunner’s book argues that enduring principles of organizing armies – regarding leadership, training, the contract between state and soldier – are “as relevant today as they were in the 4th century.” The modern context, as he notes, finds many Western governments having to rediscover those fundamentals after a long peace.

In our own time, with geopolitical tensions rising, the lesson of Nations in Arms is that a country ignores the intimate link between its military and society at its peril. A strong army is not just about budgets and hardware, but about the people in it – their motivations, values, and support from home. History’s great armies succeeded when they earned the support of their nation (be it through shared religion, ideology, patriotism, or citizen engagement) and when the nation, in turn, took care to shape and be shaped by its army. In summary, the army is a social institution as much as a war-fighting machine. The past shows that when armies and societies are aligned in purpose, they can make history – even “shape Europe,” as these five did, and leave lessons that echo across ages