hi late entry, its called northumbria due to the saxony-vikingy-jutes/angles invasion period when they were settling in england. they were split into different areas and named the areas such i.e the East Angles lived in (what is still called today) East Anglia, (the south folk and north folk became suffolk and norfolk respectively and one the most powerful peoples (along with Mercia and wessex (the west saxons)) were the northumbrians because quite simply theye lived north of the river Humber (North Humbrians = Northumbrians!!) and absolutely nowt to do with Umbria in Italy tho.