why would the Pope declare the Magna Carta invalid

This act by the pope, in support of King John, would propel England into civil war. 

   Pope Innocent III was not so innocent, but rather more like Pope Imperiously Lawless when it came to the exercise of his papal authority by which the blood of so many Christian people would be spilled in the name of the Lord - for the mortal sin of having some objections to Roman Catholicism's dictates. His reign lasted from 1198 until 1216, more than enough time to inflict a great deal of pain and bloodshed, as well as to affix great shame to Yeshua's Holy name.

   Papal authority was being undermined and challenged in some quarters of Europe, and it was his determined objective to reassert papal prepotency. He was perhaps best known for his launching of the fourth crusade, as well as his efforts to maintain universal oversight and jurisdiction atop the monarchies of Europe.

   Without getting too deep in the weeds, Innocent was very busy during his reign, not so much with spiritual matters as political. His reign would incite and manage slaughters in the form of crusades. Not only the absurd 4th crusade, but also the crusade against the so-called heresies of the Albigenses (also known as the Cathars), and initiating the brutal slaughters of the Waldensians. He also used his political and ecclesiastical weight to manage matters with the English king and the fourth Lateran Council. During his reign, Innocent built upon the political power of the papacy and was, for all intents and purposes, the most powerful man in Europe.

   The Albigensians were a semi-Christian sect, that, while they believed in the person of Jesus, were not well taught, and had no background in the Jewish foundation of Christianity. Still, they were known to behave as pious people, were well respected, and their movement had become rather widespread around southern France. However, they rejected the authority and many of the teachings of the Roman Catholic church and were thus deemed dangerous heretics. 

   It was apparently easier to kill them than to teach them, and so from the very beginning of his papacy, Innocent vigorously sought to eradicate religious dissent and launched the Albigensian Crusade which ultimately led to the slaughter of some 20,000 men, women and children across southern France, incidentally including quite a few innocent Catholics who were unfortunately caught up in the indiscriminate slaughter. The strategy apparently, was that fear would motivate them to accept the authority of the church. God was thus served. This crusade, initiated by Pope Innocent, would last from 1202, and would continue until 1229, long after his death. He left an evil legacy, including the establishment of the Dominican Order, which would ultimately plague the people of Europe with the inquisitions. His actions, parenthetically, were in no way sanctioned by scripture. (see - Devil's Handmaiden on the Warpath).

   All the while he was preparing for the campaign that would become known as the Fourth Crusade, intending to snatch Jerusalem from the hands of Muslim infidels. Taxes had to be raised in order to pay for what was expected to be an extremely expensive adventure, so envoys and emissaries were dispatched around Europe for the purpose of twisting arms and raising funds. 

   For the leadership of the armies, Innocent appealed to the Lords, knights and nobles of Europe, where the solicitations were greeted with enthusiasm among those of France, but with some reluctance from the kings of England and Germany.

   King John renounced the charter as soon as the barons departed London, and then was joined in his renunciation by a powerful ally in the person of Pope Innocent III. As soon as word reached Rome, the pope did not hesitate to join John in his repudiation of the document, seeing it as an offense against the entitlements of the church over the king, and the papal territories of England and Ireland. The Pope released John from his oath to obey the charter, calling it a “shameful and demeaning agreement, forced upon the King by violence and fear.” (The church would never engage in such coercive tactics - just ask the Cathars). And so it was that in August of 1215, Innocent III officially declared the Magna Carta invalid.  A campaign was organized to locate and burn as many copies of the charter as could be found. Today only four of the original copies remain in existence. 

   While Innocent and King John were never exactly known to be on friendly terms, and in spite of the differences that had set them apart, on these issues they stood together. John, as well as all the other monarchies of Europe, enjoyed their privileges as divine right rulers and were loath to relinquish any of their so-called God-given authority. Innocent, as pope, was the protector of divine rights, and in some sense he was the grantor of God-given authority. Any attack on the privileges of 'rule', was an attack on the entire system of governance, and in this, the Charter represented a potentially destabilizing outrage. Worse, it was said to represent a slap in the face against the very Will of God.

   The king's back-handed repudiation of the Charter was seen as an act of betrayal by the nobles, and brought about what came to be known as the First Baron's War, whereupon the barons attempted to overthrow John. It was only after King John died in 1216, that his successor, Henry III, offered a revised version of the Charter to the barons, in exchange for their allegiance, and new life was breathed back into the concept of placing limits on the power and authority of the English monarch.

   Monarchy, feudalism, fascism, socialism and communism are terms of distinction with little or no real difference, whereby an individual or a small group of individuals exercise total control over all property and all human activity within a given realm. There are no checks or balances by which they might be restrained or called to account. The common denominator is in the 'small, centralized' form of government these all favor, where all manner of corruption thrives and gets fat. The only real differences are of the size and scale of the misuse of power. In the case of the pope, his realm was the entire world by proclamation, and King John was merely one of many vassal potentates. In any of these systems of governance, those at the top of the pyramid are privileged to be above the law and never held accountable for crimes, offenses, atrocities, or acts of corruption. The control and power of the Pope in these days was indisputable, and for all practical purposes, universal. No little bit of it, not even around the margins, was Innocent ever willing to surrender. 

   Pope Innocent viewed the Magna Carta as an assault on his own authority, every bit as much as that of King John, and the pope was not going to allow any cracks to form on the monolithic facade that was the doctrine of "Divine Rights." Such an outrage could undermine the entire social order of Europe and the seat of the Roman Catholic church. Yet, in spite of the best efforts of Pope Innocent and his successors, change was beginning to percolate.

   On a side note, Innocent's Fourth Crusade became essentially a French exploit. Originally, it was supposed to transport the crusading armies to Egypt, and from there, launch an invasion against the Muslims in Jerusalem. However, the funding was insufficient to pay the Italian ships for the necessary transport. Instead, the armies, once assembled, wound up attacking the Byzantine Greek Christians at Constantinople. This, of course, was after the Great Schism of 1054 which had separated the two great Christian communions. They sacked the city in 1204, and established Latin rule over the Byzantines (Greek Christians) that would last for sixty years. This was done without the consent of Innocent, who didn't even learn of it until after the fact. Once done, however, Innocent accepted the result, believing that this might lead to reconciliation between the Roman

hints and allegations would suggest - 'divine-right' rulers stick together for mutual validation 

    In November of 1215 Innocent convened the Fourth Lateran Council, where among other things, he set the stage for the fifth crusade which was to begin in 1217. He intended it to be better planned, funded, and organized than his earlier exploit. However, he died suddenly in 1216 in the Italian city of Perugia and never got to personally see it through.

Latin church and the Greek Eastern church, a belief that would ultimately not be realized, as the schism between the two Christian communions only grew deeper and more intractable. (see - the Great Schism of 1054)

   Continuing in the rather off-topic matter of the crusades, it is also notable, and worthy of consideration, that the highly respected Jewish sage, Maimonides (Rambam) would argue later that it was preferable in the eyes of God, given the absence of the Jewish people, that the Holy Land should be occupied by Muslims rather than Roman Catholic Christians. Maimonides reasoned that God didn't want the Christians to occupy Jerusalem because everywhere the Catholics go, they bring with them their detestable idolatry, and a polytheistic concept of a triune godhead. God didn't want them polluting His Holy Land, and opposed their crusading invasions. Instead, He had them raising their hands against each other, as at Constantinople.

   The strong Islamic presence in this chosen place provided protection from these offenses. After all, this land is identified in Ezekiel 38, as a special possession in God's eyes, as the "center of the earth." So the Muslim presence was allowed to stand, by the Will of God - as a temporary place holder. Up until, such time as prophecy would be fulfilled, and the land would be restored to the Jewish people, the rightful owners. That didn't happen until 1948 (see Isaiah 66:7,8).

   The only Christian crusade that managed to succeed for a time, was the first crusade, which conquered Jerusalem in 1099. It too was temporary, however, as the city was retaken by the Muslim army led by Saladin in 1187. There would be a total of nine crusades launched against Muslim Jerusalem between the 11th and 13th centuries, but other than the first, none of them succeeded in wresting the city away from Islamic control. God's Will.

   Among other provisions, the document established a committee of barons that could meet at any time and override the will of the king should he violate, in their opinion, any of the provisions of the charter. This clause would be the undoing of the entire document, as it amounted to a check and balance on the king's authority. This of course, was a direct challenge to the supreme authority of the king and before the ink was dry, John had already determined to undo this embarrassing encroachment on his sovereignty. 

   King John had been having a troublesome relationship with the pope since 1208 when he had rejected Rome's choice of Stephan Langton as Archbishop of Canterbury. Tolerating no defiance, in response, the pope issued a decree prohibiting the English people from receiving the sacraments, and in 1209 he excommunicated John. This situation lasted until 1213 when John had a change of heart, and surrendered his kingdom to the sovereign governance of the pope. This reestablished England as a vassal state in good standing, obedient to Rome, and returned John to the good graces of the Roman Catholic pope.

   However, these matters and other matters of state had roused rebellion among the barons and nobles of England who demanded that the king affirm the "Charter of Liberties" first established in 1100 by a predecessor. John was accused of being in violation of the charter, a document that bound the king to certain laws regarding the treatment of church officials and the nobles. John refused to meet their demands and the defiance of the barons exploded into a march on London in 1215. The barons renounced their oaths of allegiance to John and were joined by an army of peasants who were simply tired of the human rights abuses imposed by unaccountable "divine right" rulers.

THE PROBLEM WITH KING JOHN

   A new charter was drawn up, and in June, 1215, they successfully forced King John to endorse the novel new document, placing the royal seal on the "Great Charter," the Magna Carta. In return, they reaffirmed their allegiance to the king and copies were made by the king's scribes for distribution around the realm so that every Englishman would know their king was bound by law.