England didn't really exist back then, there were a few different kingdoms making up what is now England, chief among them were Wessex, Mercia, East Anglia, Northumbria and Kent.

So when the vikings came, they didn't come upon a united "england" as it were, but a bunch of powerhungry warlords/kings fighting amongst themselves, if they weren't fighting the british/welsh. And even sometimes within the kingdoms itself, civil war or power struggles within their own ranks wasn't exactly uncommon either.