IN 1649 the English people did something that had never been done in the entire millennia-long history of the existence of kings and their related titles of caesar, kaiser, tsar or shah.

At the culmination of a popular revolution, they put their monarch on public trial and found him guilty of treason against the people. Charles I was then executed on a platform built outside Banqueting House in London’s Whitehall.

Kings had lost their lives before — in battle, at the hands of rivals, even killed by members of their own family. But never like this. Never had an armed people, called to battle by a parliament, defeated their sovereign and created a court to find him guilty of crimes against them. “It was not,” as the regicide Thomas Harrison later told his own trial for his part in killing the king, “a thing done in a corner.”

The greatest poet of the age, John Milton, wrote the The Defence of the English People so that in every nation on the continent it would be known that it was an act of justice.

At the same time the revolution abolished the House of Lords and declared the Commonwealth of England to be a republic.

This was not unique, for the Netherlands was already a republic but in the world of the 17th century it was remarkable that a second European country should do so amid the almost universal order of monarchy.

And it was not just that England had become a republic but how it had become a republic. Nearly a decade of political upheaval, popular mobilisation and civil war had indeed “turned the world upside down,” in the phrase contemporaries used.

The entire national church, a pillar of government as well as a religious institution, had been torn down and the Archbishop of Canterbury tried and executed. Censorship had collapsed and tens of thousands of pamphlets, newspapers, broadsheets and ballads had poured from printing presses in an uncontrollable and unprecedented torrent of free speech. 

An entire army had, in another historical first, elected its own representatives from every regiment, challenged their commanders and altered the entire political direction of the revolution.

The war that they had fought was, and remains, proportionally one of the most destructive of human life that the British Isles has ever experienced. A considerable part of the wealth and land of the defeated cavaliers was taken from them, sequestrated and used to pay for the war and given to the victors. It is hard to think of another decade in English history, with the possible exception of the 1940s, which saw so much political and social change.

On the king’s scaffold on that cold January day in 1649 stood John Harris and Richard Rumbold. The two men were from a political movement called the Levellers. It was entirely fitting that they should be there, for the movement they were part of had played a crucial role in the developing political crises of the previous decade.

From the earliest days of the revolution, and long before they were known as Levellers, the radicals of this movement were at the forefront of events.

John Lilburne, the best-known Leveller leader, was already famous to the London crowd after he was imprisoned by Charles I for distributing illegal pamphlets in the late 1630s. Richard Overton was operating a secret press that produced incendiary texts from the very earliest days of the revolution. The steadfast parliamentary ally of the Levellers, Henry Marten, shocked the king’s future political adviser by being the first MP he ever heard to advocate a republic.

As these and many other activists came to meet and organise together, they produced a torrent of the most radical literature that the revolution witnessed, often from illegal presses. They petitioned and demonstrated, fought in the war, agitated in the ranks, became spokesmen for the elected soldiers’ representatives and were often imprisoned for their pains.

There were, of course, many other political factions at work during the revolution and some of them used the same organisational tools as the Levellers. But none used all of them so consistently and effectively through the successive crises of the revolution.

And while much other political organisation focussed on the political elite, the Levellers were unique in systematically focussing on popular politics and popular mobilisation. It was this focus which, unable to rely on existing institutional networks of power, required them to develop their own organisational capacities.

The revolutionaries of the 17th century had enough support in society to pull down the ages-old institution of monarchy.

But they were still a minority. Their enemies were a substantial part of the whole society and a very substantial part of the old ruling order. The revolutionaries could find allies lower down the social strata among the working poor.

These could be engaged against this old regime but they were not themselves part of the “middling sort” of lesser gentry, merchants and craftsmen that were at the heart of the parliamentary cause.

Among this minority that made the revolution, the Levellers were themselves a minority. But they were, when the decisive crisis of the revolution arrived, a minority sufficiently bold in their ideology and effective in organisation that they could make the difference between revolution and counter-revolution.

The Levellers were first and foremost an organised group of political activists. This is perhaps a more contentious judgement than it might sound. Much interest in the Levellers has focused on the novelty of their democratic ideology.

There has also been much debate about their social origins and class location. 

These are, of course, vital and engaging areas of study, and my book is primarily a political history that focuses on the construction of Leveller organisation.

This is, after all, how they themselves confronted political problems and sought to develop their ideas in response to them. And in any case, political organisation can never be seen as immediately reducible to class locations in either appeal, membership or ideology.

This is, not least, because any class, or even a subsection of a class, can support more than one political organisation and more than one variant of an ideology. And, for this reason, exactly which organisation, and which ideology, becomes decisive at a particular historical juncture is contested and not predetermined.

• Extracted from The Leveller Revolution: Radical Political Organisation in England, 1640–1650, published by Verso Books, price £25. Available at the special price of £12.50 until January 1 from versobooks.com.