Medieval Christians collapsed Muslims, Vikings, and Picts into one undifferentiated pagan scourge.

Evidence

The historian of the twenty-first century is aware of the vast cultural and religious differences between Arab Muslims and Picts or Vikings; he is aware that Islam would survive and flourish, while the invaders from northern and eastern Europe would become Christians and integrate into the societies they had previously attacked. The Northumbrian or Frank of the eighth century could not know this: he saw God’s scourge falling on him from all sides and sought an explanation in the sins of Christians; he was not interested in studying the different beliefs of these “pagan” invaders. — John V. Tolan, Saracens, 456

Categorization

• XREF: Parallels the reader’s moral-panic work: the category of ‘enemy’ flattens distinctions among very different groups, just as moral panics lump distinct behaviors into one menace.
• DEEPTHINKING: The asymmetry of hindsight — what later historians can distinguish, contemporaries could not — is a genuinely dense observation about how categories form at the time versus after the fact.