Fred, England has been the 'dominant' partner - usually - among the nations of Britain for the simple reason that its population dwarfs those of the other three combined. Thus, one can understand why, in historic times, foreign nationals such as Americans - and many Englishmen! - referred to the whole Union as 'England'.
A classic example was Nelson's signal at the Battle of Trafalgar about 'England' expecting every man to do his duty, despite the fact that his ‘British' vessels were manned by over 18,000 sailors, about one in ten of whom was not even British, never mind English! HMS Bellerophon alone, with a complement of 540, had twelve nationalities aboard, including Swedes, Danes, West Indians, Portuguese, Indians and even three Frenchmen!
In this day and age, there is surely no need for Americans (or Englishmen) to go on with the narrow approach to what our country's name actually IS.
As regards St George's flag, it has been sullied in exactly the same way as an innocent Asiatic religious symbol was hijacked by the Nazis and became the swastika. A pity, but there you go.