How far can things slide? For those seeking an answer, Ian Gentles has provided a service. The republication of his The New Model Army (1992) — updated to reflect 30 years of scholarship since and with a new subtitle, Army of Revolution — gives a thought-provoking account of what happened when things slid about as far as they could in the period of the English Civil Wars.

The book is an authoritative and engaging narrative of the sudden rise, the turbulent reign and abrupt demise of the New Model Army. The New Model Army came into existence through an Act of Parliament in January 1645 as a response to both the faltering performance and loyalty of the parliamentary forces. It was an appropriately radical solution for a radical cause, intending to deliver discipline, ideological purity and military effectiveness in one go. The army would, for the first time, be a standing, national army with a funding stream agreed by Parliament and leaders who, through the ‘self-denying ordnance’, would be banned from also sitting in either House or Parliament. Professionalised and depoliticised, the New Model Army set precedents which would endure long beyond its cause. Its ironic place as the foundation stone of Britain’s conquering imperial armies is also evidenced more graphically by its adoption of the ‘red coat’, which would be the signature of the British Army for the next 200 years.

Gentles’ book is an exploration of the politics behind the New Model Army as much as of its performance and capabilities. It also examines what motivated the rank and file and the ‘grandees’ who led it (not always the same thing), and the dominant role played by the concept of ‘godliness’, the nearest thing the New Model Army had to a revolutionary mantra. The book contains both detailed accounts of the army’s processes and manoeuvres, with helpful maps of battles and campaigns, and a strong sense of place and geography (such as the important role of London public houses in the torrid politics of the time). But what gives it a sharp, contemporary relevance is its careful, dispassionate study of how political conviction and righteousness, once popularised, inevitably and quickly lead to tyranny.

Was Cromwell a tyrant? In his overall judgements of both Cromwell and the New Model Army, Gentles is balanced. He spares neither of them responsibility for the massacres in Ireland, in particular at Drogheda, nor for the callousness with which they administered justice among their own ranks, including exemplary executions and the banishing of offenders to certain death on the Caribbean plantations. Against that, he notes that there were very few political prisoners under Cromwell, and the death penalty was only administered to those who sought actively to overthrow the Commonwealth. But in many familiar respects, Cromwell’s rule was tyrannous: his power was supreme, and so, too, was his conviction of his own rightness. He controlled the democratic process (vetting all MPs for their loyalty) and the armed forces which he led; and he actively proscribed popular entertainment and forms of worship with which he did not agree. A man of high principle and vision, he nonetheless presided over a country which slid not just into civil war but regicide, cultural warfare and a period of prolonged armed factionalism which, in the memorable phrase of the contemporary thinker Thomas Hobbes, proved to be ‘a war of all against all’. When things slide even with a god-fearing man of principle at the helm, they slide very far and very fast.

The New Model Army was both the agent through which Cromwell’s power was exercised and a natural outgrowth of his agenda. Militarily talented and personally courageous, the military was for Cromwell both a necessary and congenial instrument of state. The relationship was mutual. Even at its most unruly and rebellious, the army remained loyal if not obedient to Cromwell. In victory, such as at Worcester over Charles I, or Dunbar, where Cromwell’s brilliance as a general saved the army from what looked like annihilation, Cromwell was adored. In defeat, Cromwell took the army’s part and blamed himself.

The New Model Army bore the stamp of its creator in its discipline, but also in one important aspect which Gentles draws out dextrously throughout the book: it shared his religious zealotry. Officers and men fasted and prayed before battles and key decisions. Cromwell led them into battle shouting, ‘In the name of the Lord God of Hosts’. A victory was a further sign of God’s pleasure, a defeat of the army’s and Cromwell’s iniquity. The belief that the army was the instrument of God was intense and matched only by the belief that its enemies were not only the enemies of the people but, by definition, godless. That included opposing Christian sects and, above all, Catholics. Cromwell exhorted the troops to remember that their enduring enemy was Spain. It was the shared sense that Catholic Ireland was Spain’s back door which drove Cromwell’s determination to subdue it by force.

Cromwell and his army are easy to caricature but their zealotry is given shade and texture by Gentles. Deep conviction did not always lead him into hostility towards his religious opponents. He chose in Scotland, where much was at stake, to follow up his victories not by persecution but by an active engagement in disputation with the Presbyterians. He and his officers responded to sermons with their own exegesis, often exhausting their opponents by the length and density of their arguments.

Gentles reminds us, too, of the accidental legacies of the New Model Army. The ill-fated expedition against the Spanish possession in the Caribbean failed entirely in Hispaniola, where the army was lucky to survive. But in Jamaica, where they sought to redeem their reputation, they won and instituted what proved to be 300 years of British rule. Their legacy in Ireland was equally long and, if possible, more bitter. There are other transatlantic references which are reminders that England was, by the 1650s, a rising global power even if the established powers regarded her with disdain. Barbados features frequently, as a source of manpower for the New Model Army’s Caribbean campaign and a destination for convicts. After the final defeat of the New Model Army, several of its leaders fled to New England to seek refuge in the colonies recently founded by the puritan Pilgrim Fathers. The diplomatic shock waves of the New Model Army could be felt across Europe. Stunned at their execution of Charles, most monarchies regarded Cromwell and his army with the same mixture of incomprehension and terror as England would Napoleon and the Revolutionary Army a century later. In its ability to terrify incumbent power, the New Model Army was genuinely revolutionary.

While Gentles’ subject is the Model Army, the genius of Cromwell and his towering will inevitably dominate. Yet the closing acts of the New Model Army’s drama belong to Major General George Monck, whose serpentine career reflects the political uncertainties and ambiguities of the time. A professional soldier under Charles I, he was captured fighting for the Royalists at Nantwich but later recruited by Cromwell and given commands in Ireland and Scotland, only to prove, after Cromwell’s death, the key player in the Restoration. Monck both led the New Model Army and ultimately defeated it, and was personally loyal to Cromwell and to the Crown. Gentles portrays him as militarily and administratively gifted (he was responsible for the key victories of the New Model Army in the Scottish campaign of the 1650s and subsequently governed Scotland with vigour and rigour) and politically astute. The chapter covering Monck’s subtle transference of his loyalty from the Commonwealth to Charles II, raising an army which, ultimately, he did not need to use, is a study in exquisite political timing. Gentles captures the tension felt in England and Scotland as the political wind started to back. Monck’s achievement, in ensuring the peaceful restoration of the House of Stuart, against which he had taken up arms, is breath-taking, even at this distance. The calculations over loyalty he made on a daily basis would equal those in the most complex of contemporary political campaigns. He is the ultimate survivor: he emerged not only with his head but with it adorned by a ducal coronet. Neither did he lose his lands, as many New Model Army’s leaders had done, in clear breach of the Treaty of Breda, but had them lavishly augmented by a grateful monarch. As the New Model Army melted away, Monck stepped forward to sweep the board.

Gentles charts the rapid demise of the New Model Army after the death of Cromwell with insight. The army lacked institutions or leaders to ensure its survival; it had overplayed its hand in enforcing its puritan agenda; it was still in dispute with Parliament over pay; and, above all, it was simply unpopular. Ironically, the army which had sought to be a people’s army ended up representing only a narrow and bigoted band of English society. It was opposed by members of Parliament, the elected representatives, with whom it was in constant dispute over pay, and by those such as the Levellers, who thought it insufficiently puritan. In the end, it proved to be a niche army, able to fight a clearly defined, incumbent enemy, when led by able generals. But it could not manage the transition to either a peace-time security or administrative force with institutionalised leadership. It lacked what it most frequently criticised in Parliament, good governance and accountability. When the zeal unleashed by the fight against the Royalists ebbed, the army found new enemies who were less motivating and required adaptations it was ill equipped to make. The New Model Army had its moment, as did Cromwell, but it could not overwhelm the English institutions (the Crown, the City of London, the Church) as they inexorably reasserted themselves.

Gentles makes a convincing case that the New Model Army was an agent of revolution. But its revolution, unlike the religious conviction, was brief and shallow. Large numbers of its members, as Gentles notes, continued to believe in the ‘good old cause’ after they had been demobbed, but the moment had gone. It was Monck who spotted that the revolution and the cause had run their course and the political wind had changed: the godly, righteous England so hoped for by Cromwell and his deputies was an aspiration too far. He read both the domestic politics and the geopolitics of continental Europe with remarkable accuracy. If there is a lesson for troubled democracies fearful of a slide into something much worse, it may be that the pragmatic statesman who commands force but does not use it is more valuable than the zealot, however godly.