… or at least he tried to butcher them. On this day 800 years ago, King John was compelled to sign Magna Charta, formally accepting a limit to his prerogative to ravage everything in England. But the ink on his signature was barely dry before he brought in foreign forces and tried to wipe out the barons who had compelled him to sign the Charta. The English almost lost their newly-recognized rights within months of the signing because they were not sufficiently suspicious of the King. As David Hume noted in his magisterial History of England, “The ravenous and barbarous mercenaries, incited by a cruel and enraged prince, were let loose against the estates, tenants, manors, houses, parks of the barons, and spread devastation over the face of the kingdom. Nothing was to be seen but the flames of villages and castles reduced to ashes, the consternation and misery of the inhabitants, tortures exercised by the soldiery to make them reveal their concealed treasures…”
Few people recall that Pope Innocent speedily sought to annul the charter and formally absolved King John of any obligation to obey Magna Charta. English liberties received a boost from the death of King John less than a year after Runnymede.
The real lesson of Magna Charta is that solemn pledges do not make tyrants trustworthy. Similarly, American presidents are required to pledge upon taking office that “I do solemnly swear that I will faithfully… preserve, protect and defend the Constitution of the United States.” At this point, that oath does little more than spur cheers from high school civics teachers. It has been more than 40 years since any president paid a serious price for trampling the law. And presidents have a prerogative to trample constitutional rights as long as they periodically proclaim their devotion to democracy.
In the final realm, Magna Charta was simply a political promise – and it would only be honored insofar as private courage, resolution, and weaponry compelled sovereigns to limit their abuses.
Here’s David Hume’s account of what happened after Magna Charta was signed (copied from the excellent Liberty Fund online version of Hume’s history):
John seemed to submit passively to all these regulations, however injurious to majesty: He sent writs to all the sheriffs, ordering them to constrain every one to swear obedience to the twenty-five barons.s He dismissed all his foreign forces: He pretended, that his government was thenceforth to run in a new tenor, and be more indulgent to the liberty and independance of his people. But he only dissembled, till he should find a favourable opportunity for annulling all his concessions. The injuries and indignities, whichEdition: current; Page:  he had formerly suffered from the pope and the king of France, as they came from equals or superiors, seemed to make but small impression on him: But the sense of this perpetual and total subjection under his own rebellious vassals, sunk deep in his mind, and he was determined, at all hazards, to throw off so ignominious a slavery.t He grew sullen, silent, and reserved: He shunned the society of his courtiers and nobles: He retired into the Isle of Wight, as if desirous of hiding his shame and confusion; but in this retreat he meditated the most fatal vengeance against all his enemies.u He secretly sent abroad his emissaries to inlist foreign soldiers, and to invite the rapacious Brabançons into his service, by the prospect of sharing the spoils of England, and reaping the forfeitures of so many opulent barons, who had incurred the guilt of rebellion, by rising in arms against him.w And he dispatched a messenger to Rome, in order to lay before the pope the Great Charter, which he had been compelled to sign, and to complain, before that tribunal, of the violence, which had been imposed upon him.x??
Innocent, considering himself as feudal lord of the kingdom, was incensed at the temerity of the barons, who, though they pretended to appeal to his authority, had dared, without waiting for his consent, to impose such terms on a prince, who, by resigning to the Roman pontiff his crown and independance, had placed himself immediately under the papal protection. He issued, therefore, a bull, in which, from the plenitude of his apostolic power, and from the authority, which God had committed to him, to build and destroy kingdoms, to plant and overthrow, he annulled and abrogated the whole charter, as unjust in itself, as obtained by compulsion, and as derogatory to the dignity of the apostolic see. He prohibited the barons from exacting the observance of it: He even prohibited the king himself from paying any regard to it: He absolved him and his subjects from all oaths, which they had been constrained to take to that purpose: And he pronounced a general sentence of excommunication against every one, who should persevere in maintaining such treasonable and iniquitous pretensions.y
The king, as his foreign forces arrived along with this bull, now ventured to take off the mask; and, under sanction of the pope’s decree, recalled all the liberties which he had granted to his subjects, and which he had solemnly sworn to observe. But the spiritual weapon was found upon trial to carry less force with it, than he had reason from his own experience to apprehend. The primate refused to obey the pope in publishing the sentence of excommunication against the barons; and though he was cited to Rome, that he might attend a general council, there assembled, and was suspended, on account of his disobedience to the pope, and his secret correspondence with the king’s enemies.z Though a new and particular sentence of excommunication was pronounced by name against the principal barons;a John still found, that his nobility and people, and even his clergy, adhered to the defence of their liberties, and to their combination against him: The sword of his foreign mercenaries was all he had to trust to for restoring his authority.??
The barons, after obtaining the Great Charter, seem to have been lulled into a fatal security, and to have taken no rational measures, in case of the introduction of a foreign force, for reassembling their armies. The king was from the first master of the field; and immediately laid siege to the castle of Rochester, which was obstinately defended by William de Albiney, at the head of a hundred and forty knights with their retainers, but was at last reduced by famine.30th Nov. John, irritated with the resistance, intended to have hanged the governor and all the garrison; but on the representation of William de Mauleon, who suggested to him the danger of reprizals, he was content to sacrifice, in this barbarous manner, the inferior prisoners only.b The captivity of William de Albiney, the best officer among the confederated barons, was an irreparable loss to their cause; and no regular opposition was thenceforth made to the progress of the royal arms. The ravenous and barbarous mercenaries, incited by a cruel and enraged prince, were let loose against the estates, tenants, manors, houses, parks of the barons, and spread devastation over the face of the kingdom. Nothing was to be seen but the flames of villages and castles reduced to ashes, the consternation and misery of the inhabitants,Edition: current; Page:  tortures exercised by the soldiery to make them reveal their concealed treasures, and reprizals no less barbarous, committed by the barons and their partizans on the royal demesnes, and on the estates of such as still adhered to the crown. The king, marching through the whole extent of England, from Dover to Berwic, laid the provinces waste on each side of him; and considered every state, which was not his immediate property, as entirely hostile and the object of military execution. The nobility of the north in particular, who had shewn greatest violence in the recovery of their liberties, and who, acting in a separate body, had expressed their discontent even at the concessions made by the Great Charter; as they could expect no mercy, fled before him with their wives and families, and purchased the friendship of Alexander, the young king of Scots, by doing homage to him.
The barons, reduced to this desperate extremity, and menaced with the total loss of their liberties, their properties, and their lives, employed a remedy no less desperate; and making applications to the court of France, they offered to acknowledge Lewis, the eldest son of Philip, for their sovereign; on condition, that he would afford them protection from the violence of their enraged prince. Though the sense of the common rights of mankind, the only rights that are entirely indefeasible, might have justified them in the deposition of their king; they declined insisting before Philip, on a pretension, which is commonly so disagreeable to sovereigns, and which sounds harshly in their royal ears. They affirmed, that John was incapable of succeeding to the crown, by reason of the attainder, passed upon him during his brother’s reign; though that attainder had been reversed, and Richard had even, by his last will, declared him his successor. They pretended, that he was already legally deposed by sentence of the peers of France, on account of the murder of his nephew; though that sentence could not possibly regard any thing but his transmarine dominions, which alone he held in vassalage to that crown.1216. On more plausible grounds, they affirmed, that he had already deposed himself by doing homage to the pope, changing the nature of his sovereignty, and resigning an independant crown for a see under a foreign power. And as Blanche of Castile, the wife of Lewis, was descended by her mother from Henry II. they maintained, though many other princes stood before her in the order of succession, that they had not shaken off the royal family, in chusing her husband for their sovereign.??Edition: current; Page: 
Philip was strongly tempted to lay hold on the rich prize which was offered to him. The legate menaced him with interdicts and excommunications, if he invaded the patrimony of St. Peter, or attacked a prince, who was under the immediate protection of the holy see.c But as Philip was assured of the obedience of his own vassals, his principles were changed with the times, and he now undervalued as much all papal censures, as he formerly pretended to pay respect to them. His chief scruple was with regard to the fidelity, which he might expect from the English barons in their new engagements, and the danger of entrusting his son and heir into the hands of men, who might, on any caprice or necessity, make peace with their native sovereign, by sacrificing a pledge of so much value. He therefore exacted from the barons twenty-five hostages of the most noble birth in the kingdom;d and having obtained this security, he sent over first a small army to the relief of the confederates; then more numerous forces, which arrived with Lewis himself at their head.
The first effect of the young prince’s appearance in England was the desertion of John’s foreign troops, who, being mostly levied in Flanders, and other provinces of France, refused to serve against the heir of their monarchy.e The Gascons and Poictevins alone, who were still John’s subjects, adhered to his cause; but they were too weak to maintain that superiority in the field, which they had hitherto supported against the confederated barons. Many considerable noblemen deserted John’s party, the earls of Salisbury, Arundel, Warrene, Oxford, Albemarle, and William Mareschal the younger: His castles fell daily into the hands of the enemy: Dover was the only place, which, from the valour and fidelity of Hubert de Burgh, the governor, made resistance to the progress of Lewis:f And the barons had the melancholy prospect of finally succeeding in their purpose, and of escaping the tyranny of their own king, by imposing on themselves and the nation a foreign yoke. But this union was of short duration between the French and English nobles; and the imprudence of Lewis, who, on every occasion, showed too visible a preference to the former, encreased that jealousy, which it was so natural for the latter to entertain in their present situation.g The viscount of Melun, too, itEdition: current; Page:  is said, one of his courtiers, fell sick at London, and finding the approaches of death, he sent for some of his friends among the English barons, and warning them of their danger, revealed Lewis’s secret intentions of exterminating them and their families as traitors to their prince, and of bestowing their estates and dignities on his native subjects, in whose fidelity he could more reasonably place confidence.h This story, whether true or false, was universally reported and believed; and concurring with other circumstances, which rendered it credible, did great prejudice to the cause of Lewis. The earl of Salisbury and other noblemen deserted again to John’s party;i and as men easily change sides in a civil war, especially where their power is founded on an hereditary and independant authority, and is not derived from the opinion and favour of the people, the French prince had reason to dread a sudden reverse of fortune. The king was assembling a considerable army, with a view of fighting one great battle for his crown; but passing from Lynne to Lincolnshire, his road lay along the sea-shore, which was overflowed at high water; and not chusing the proper time for his journey, he left in the inundation all his carriages, treasure, baggage, and regalia. The affliction for this disaster, and vexation from the distracted state of his affairs, encreased the sickness under which he then laboured; and though he reached the castle of Newark, he was obliged to halt there, and his distemper soon after put an end to his life,17th Octob. Death and character of the king. in the forty-ninth year of his age, and eighteenth of his reign; and freed the nation from the dangers, to which it was equally exposed, by his success or by his misfortunes.