Contrary to what's often taught in schools, Anglo-Saxon England was firmly and thoroughly engaged with continental Europe politically, culturally and economically. From the seventh century onwards, the network of wic sites (Ipswich, Norwich, Southampton [Hamwic], etc.) develops organically as an extensive series of trade ports and productive sites across both sides of the English Channel.
Political alliance and communication with Europe was constant; in 597, Æthelberht of Kent was married to a Merovingian princess, and in the 870, Offa of Mercia corresponds regularly with Charlemagne, even suggesting a marriage between his son and Charles' daughter. Much was due to the close relationship between England and Rome: English pilgrims to Rome were sufficiently common that there was an 'English Quarter' in Rome to which Burgred of Mercia retired following his defeat at the Battle of Repton in 873, and Alfred the Great later founded a hospital there. Alfred himself had been to visit the Pope as a child, and later returned through Europe, visiting the Carolingian court of Charles the Bald in Paris. Charlemagne's Palatine School, established in Aachen to teach the children of his nobility, was until 804 run by Alcuin of York, a famous Anglo-Saxon cleric and teacher, who introduced Anglo-Saxon philosophy and also spearheaded Charles' religious reforms.
In Old English, the term for war was wig or wiga. Why this term was displaced by werre isn't exactly clear, although Old English had previously adopted extensive grammatical structures and pronounciations from native Brythonic in its infancy, so werre may have already been synonymously in use by the late Anglo-Saxon period.