What happened — and why
Vikings: destroyers and creators
Raids on the monasteries of Ireland, France, and England. Lindisfarne (793) marks the start of the age. Charlemagne has just died, his empire is falling apart, and no one is left to defend it.
The philosophical cause
Monasteries were the richest institutions of the era and the keepers of manuscripts. The irony: by destroying monasteries the raiders unwittingly hastened the movement of texts deeper into the continent.
By the century's end the Vikings themselves become Christians and found states of their own: Normandy, Kievan Rus (the Varangians were Vikings), and kingdoms across Britain.
Cyril and Methodius create Slavic writing (863)
The brothers from Thessalonica create the Glagolitic script, the first alphabet for the Slavic languages. They translate the Gospel and the liturgical books. Their mission goes to Moravia.
The philosophical cause
Cyril — Before them, worship was conducted only in Latin, Greek, and Hebrew. Cyril insisted: God speaks in every language. It was a revolutionary claim.
The Cyrillic script, derived from Glagolitic, would become the writing system for dozens of peoples. The conversion of Rus in 988 would have been impossible without this foundation.
The breakup of Charlemagne's empire: the birth of Europe
The Treaty of Verdun (843): three grandsons of Charlemagne divide the empire. West Francia foreshadows France. East Francia foreshadows Germany. The border between them stayed unchanged until the 20th century.
The philosophical cause
Feudal logic: power rests on personal loyalty, not on an abstract state. When a strong ruler dies, the empire is divided.
Europe as a system of competing states rather than a single empire was born in the 9th century. That very competition gave it a dynamism that neither China nor Rome ever had.