England had a solid foundation of domination laid down by the Romans. Even after the fall of the Roman Empire it's laws, financial systems, and political structures were adopted by many of its former holdings. Now it's a long jump in time from the fall of Rome to the first United English Kingdom of Alfred the Great. In fact leading up to Alfred there had been multiple incursions by many people into England, the Vikings nearly conquered all of the early English kingdoms and even those kingdoms were conquests of the Angles and Saxons.