Christian Conversion—The central organizing principle of Europe during its rise from the remnants of the Roman Empire to the modern nations of Europe was the Christian religion. The barbarian tribes of Hispania and Gaul had been Christianized to some extent during Roman times, but many of the Germanic and Slavic tribes in the north of Europe were not brought under the influence of Christianity until much later. With the "conversion" of a country to Christianity came many trappings of Christian civilization, including an educated class of clerics, Roman legal institutions, Christian teachings on morals, and most importantly for regional kings—the recognition of their legitimacy. That is, a local ruler who paid homage to the Church and other Christian overlords could be recognized as a legitimate ruler throughout all of Christendom and had less to fear from both internal rebellions and external invasions. Becoming part of the Christian family of nations did not eliminate these threats, but it enhanced the stability of the ruling classes of Europe and helped create the conditions necessarily for peace, commerce, and progress.
Charlemagne and the Franks—Many important milestones of the early years of the European Middle Ages relate to the conversion of barbarian tribes to Catholic Christianity, and the defense of already Christian territories from pagan hosts. The conversion of Clovis, king of the Franks, to Catholic Christianity was of utmost importance. During the 7th and 8th centuries, the Franks kept the Moors of Spain at bay, defended Catholic interests in Western Europe, and converted pagan tribes to the Christian cause. In 800 A. D., the greatest of the Frankish kings, Charlemagne, was crowned Holy Roman Emperor by the pope. Charlemagne not only helped fend off the Moslems in the Iberian Peninsula, but also conquered Northern Italy from the pagan Lombards, and forcibly converted great swaths of Saxony to Christianity. The territory he controlled consisted mainly of modern day France, Germany, and Italy, the central territories of Western Europe.
Once the Holy Roman Empire was established, it faced several long-term threats. First, the threat of Vikings, or barbarian invasion from the North; second, the growing threat of Moslem aggression in the Mediterranean regions; and third strife between the Church and various princes. Although specific conflicts related were regional, the overall threats were common to all of Christian Europe.
Vikings and Normans—Between the years 900 and 1200 A. D., a hardy race of pagan Norsemen over-ran much of Northern Europe. After decades of plunder and rampage, the Vikings were won over the Christian cause, less by armed resistance than by acculturation. They frequently conquered Christian lands but ended up marrying Christian women, ruling over Christian subjects, and raising Christian children. As second and third generation Viking rulers became Christianized, their adopted religion spread to their native lands, and eventually all of Scandinavia became Christian. The most important of the Viking rulers were the Normans, who ruled over Northern France and eventually conquered all of Britain and much of Italy. The Norsemen even formed several "crusader kingdoms" in the Middle East, and founded a dynasty in Russia.
During this same period, Christianity was spreading to the Slavic regions of eastern Europe. Poland, Russia, Hungary, Bohemia, and Lithuania were converted to Christianity by both Catholic and Orthodox missionaries. These regions had never been influenced by Roman civilization, and did not have written languages until they were converted to Christianity. Even though they were late to adopt the customs and culture of Western Europe, they were important Christian bulwarks against the advancing Mohammed and Mongol threats from the east.
The Islamic Threat—The Christian church had been fighting off schisms and heresies for hundreds of years when the Islamic threat took hold in the outermost regions of Christendom. Within fifty years of the death of Mohammed the new religion had swept all of the Middle East, Egypt and North Africa. Soon after the Moors conquered most of the Iberian Peninsula and threatened all of Europe. The Franks were key in turning the Mohammedan tide in Spain, and the Eastern Empire, centered in Constantinople, provided a buffer-state between the Moslem states of the Middle East and southeast Europe. Without these bulwarks, Europe almost certainly would have been over-run.
The Mohammedan Abbasid dynasty (750 to 1258 A.D.) was centered in Baghdad and ruled over a highly civilized region. The Abbasids tolerated Christian travelers, so for hundreds of years commerce and religious pilgrimages to the holy land continued unhindered. Eventually, however, the Abbasids lost ground to a more radical, less civilized tribe from central Asia. The "Turkish" Moslems conquered both Christian and Abbasid territories and eventually formed the Ottoman Empire. It was this branch of Islam which threatened Europe from the south and East for much of the Middle Ages.
The Crusades, which occurred during the eleventh and twelfth centuries, were a series of campaigns by Christian Europeans intended to reclaim the Holy Lands from Turkish Moslems. When these campaigns failed, the Turks were able to consolidate their territories in Asia Minor and invade southern Europe. Much of the Balkans fell to the Turks in the 12th and 13th centuries, and Constantinople fell in 1453. The Ottoman Turks continued to threaten Eastern Europe throughout the 15th and 16th centuries, and were not driven from the Balkan Peninsula until the 19th century. Many Christian heroes of the Middle Ages gained their renown from fighting to drive back the Mohammedans and maintain a Christian culture within Europe.
Church vs. State—The Christian religion sees the world as having both a spiritual realm and a material realm, and the mediaeval Church claimed the "spiritual" realm as its domain, while acknowledging the rights of princes over their earthly kingdoms. The border between material and spiritual reality, however, has ever been a messy one. From the princes' point of view, the church provided important services, but should be made to serve the interests of the state. From the Church's point of view, the princes ruled by the grace of God and were beholden to promote the interests of the Church. This conflict of interests has existed throughout the life of the church, but in the Middle Ages when the church held so much influence that an ex-communicated prince could not command the allegiance of his subjects, the controversy raged in many forms.
In Germany and Italy, the investiture controversy was essentially a conflict about who should control church property. Princes thought that since their armies were needed to protect church properties, they should be allowed to appoint bishops that would serve their interests. The church thought that it should be able to appoint bishops that were faithful to the papacy and Christian interests. Since church properties generated a great deal of income, this was more than a philosophical disagreement and many wars were fought over the issue. In France the same pressures applied, but the conflict was resolved for a long time by outright theft of the papacy. The Avignon Papacy was a hundred year period during which the King of France selected and maintained the Pope in his own domains, and even when the papacy was restored to Rome, it became largely a pawn of the Italian princes.
The result of princes appointing and controlling bishops was inevitable corruption. Church offices and their revenues became tools of the government, and a great deal of the money and land donated to the church for charitable purposes fell under the control of feckless nobles. The astounding factor in this situation was not the deplorable state of morals within the church hierarchy but the fact that in local parishes so much charitable work continued to get done, and so many pious and faithful servants of God were still attached to the religious life.
The Reformation—The widespread corruption within the church was in blatant conflict with the dogmas the church was bound to uphold. Sincere reformers from both inside and outside the church arose, but the extreme wealth of the church was a magnet but for opportunists of all stripes. The manner in which the reformation of the Catholic church occurred, therefore, varied by region, and had a great deal to do with local politics as well as theology.
In Germany, where Luther held sway, the church properties of kingdoms that broke away from Rome fell under the control of the princes, but much of the Church organization remained intact. In the Netherlands, the Calvinist variety of Christianity became a rallying point against the oppressions of Hapsburg Spain. Calvinism was especially popular with the merchant classes in independent cities throughout Europe, where local leaders opposed all hierarchy and rituals of the "papists" and sought to appoint church elders by popular election. In France, the Huguenot movement was almost crushed by the clever machinations of the mastermind, Richelieu, who sought to promote religious unity at home, while he sowed discord among his enemies by promoting Protestant causes in Germany.
The devastating Thirty Years War resulted in the Peace of Westphalia, which granted legitimacy and recognition to many of the Protestant governments of Europe. Its primary effect, however, was political: it resulted in a strengthened Bourbon France and a greatly weakened Hapsburg Empire. From this point on, the Hapsburg Empire was no longer the predominant power in Europe. Politics were driven by "balance of power" considerations, as Austria, France, Russia, Russia, and England maneuvered to protect their political interests in a continent where the ideal of religious unity could no longer serve as an effective break on nationalistic ambition.