information:extraction, linguistic:paraphrasing
Early Middle Ages

During the decline of the Roman Empire, Europe entered a long period of change arising from what historians call the " Age of Migrations ". There were numerous invasions and migrations amongst the Ostrogoths, Visigoths, Goths, Vandals, Huns, Franks, Angles, Saxons, Slavs, Avars, Bulgars, Vikings, Pechenegs, Cumans, and Magyars. Renaissance thinkers such as Petrarch would later refer to this as the "Dark Ages".

Isolated monastic communities were the only places to safeguard and compile written knowledge accumulated previously; apart from this, very few written records survive. Much literature, philosophy, mathematics, and other thinking from the classical period disappeared from Western Europe, though they were preserved in the east, in the Byzantine Empire.

While the Roman empire in the west continued to decline, Roman traditions and the Roman state remained strong in the predominantly Greek-speaking Eastern Roman Empire, also known as the Byzantine Empire. During most of its existence, the Byzantine Empire was the most powerful economic, cultural, and military force in Europe. Emperor Justinian I presided over Constantinople's first golden age: he established a legal code that forms the basis of many modern legal systems, funded the construction of the Hagia Sophia and brought the Christian church under state control.

From the 7th century onwards, as the Byzantines and neighbouring Sasanid Persians were severely weakened due to the protracted, centuries-lasting and frequent Byzantine–Sasanian wars, the Muslim Arabs began to make inroads into historically Roman territory, taking the Levant and North Africa and making inroads into Asia Minor. In the mid-7th century, following the Muslim conquest of Persia, Islam penetrated into the Caucasus region. Over the next centuries Muslim forces took Cyprus, Malta, Crete, Sicily, and parts of southern Italy. Between 711 and 720, most of the lands of the Visigothic Kingdom of Iberia were brought under Muslim rule—save for small areas in the northwest (Asturias) and largely Basque regions in the Pyrenees. This territory, under the Arabic name Al-Andalus, became part of the expanding Umayyad Caliphate. The unsuccessful second siege of Constantinople (717) weakened the Umayyad dynasty and reduced their prestige. The Umayyads were then defeated by the Frankish leader Charles Martel at the Battle of Poitiers in 732, which ended their northward advance. In the remote regions of north-western Iberia and the middle Pyrenees the power of the Muslims in the south was scarcely felt. It was here that the foundations of the Christian kingdoms of Asturias, Leon, and Galicia were laid and from where the reconquest of the Iberian Peninsula would start. However, no coordinated attempt would be made to drive the Moors out. The Christian kingdoms were mainly focused on their own internal power struggles. As a result, the Reconquista took the greater part of eight hundred years, in which period a long list of Alfonsos, Sanchos, Ordoños, Ramiros, Fernandos, and Bermudos would be fighting their Christian rivals as much as the Muslim invaders.

During the Dark Ages, the Western Roman Empire fell under the control of various tribes. The Germanic and Slav tribes established their domains over Western and Eastern Europe, respectively. Eventually the Frankish tribes were united under Clovis I. Charlemagne, a Frankish king of the Carolingian dynasty who had conquered most of Western Europe, was anointed " Holy Roman Emperor " by the Pope in 800. This led in 962 to the founding of the Holy Roman Empire, which eventually became centred in the German principalities of central Europe.

East Central Europe saw the creation of the first Slavic states and the adoption of Christianity (c. 1000 CE). The powerful West Slavic state of Great Moravia spread its territory all the way south to the Balkans, reaching its largest territorial extent under Svatopluk I and causing a series of armed conflicts with East Francia. Further south, the first South Slavic states emerged in the late 7th and 8th century and adopted Christianity: the First Bulgarian Empire, the Serbian Principality (later Kingdom and Empire), and the Duchy of Croatia (later Kingdom of Croatia). To the east, Kievan Rus' expanded from its capital in Kiev to become the largest state in Europe by the 10th century. In 988, Vladimir the Great adopted Orthodox Christianity as the religion of state. Further east, Volga Bulgaria became an Islamic state in the 10th century, but was eventually absorbed into Russia several centuries later.