Question: Halfdan Ragnarsson was a commander of a coalition of Norse warriors, originating from where?
Sentence (from "Great Heathen Army"): The Great Viking Army or Great Danish Army, known by the Anglo-Saxons as the Great Heathen Army (OE: "mycel hæþen here"), was a coalition of Norse warriors, originating from Denmark (and likely also from Sweden and Norway) who came together under a unified command to invade the four Anglo-Saxon kingdoms that constituted England in AD 865.
Relevant evidence: Yes