Complex sentence: The Vikings were not a major threat to Wessex during Æthelwulf's reign; however, in 843 he was defeated in a battle at Carhampton in Somerset, but achieved a major victory at the Battle of Aclea in 851.
Split into simpler sentences: The Vikings were not a major threat to Wessex during Æthelwulf's reign. In 843 he was defeated in a battle at Carhampton in Somerset, but achieved a major victory at the Battle of Aclea in 851.