James Alexander Thom said this quote

A novel, or so-called “fiction,” if deeply researched and conscientiously written, might well contain as much truth as a high-school history textbook approved by a state board of education. But having been designated “historical fiction” by its publisher, it is presumed to be less reliably true than that textbook. If fiction were defined as “the opposite of truth,” then much of the content of many approved historical textbooks could be called “historical fiction.”But fiction is not the opposite of truth. Fiction means “created by imagination.” And there is plenty of evidence everywhere in literature and art that imagination can get as close to truth as studious fact-finding can.

~ James Alexander Thom

my own definition of bad historical fiction hits these points:It fails to transport the reader to a former time.It fails to put the reader in another place.It fails to bring characters to life.It fails to make the reader shiver, sweat, sniffle, sneer, snarl, weep, laugh, gag, ache, hunger, wince, yearn, lust, lose sleep, empathize, hate, or need to go potty.It seems dubious.It has characters who seem too good or too bad to be true.It has anachronisms.It has clichés and stereotypes.Its writing style distracts the reader from the narrative.It takes historic license with times and facts.It is pointless.It is carelessly written.It is easy to put down.

~ James Alexander Thom

Before you're ready to tell that story well, you might have to study and learn the equivalent of an entire specialized college education on the society in which your story takes place, because all sorts of things were happening that you need to understand before you can even begin to tell a story in that milieu.

~ James Alexander Thom

Mortmain is an old French word that should be tattooed on the inside of any historical novelist's skull. This wonderful and terrible word means “dead hand.” Its definition is: “The influence of the past regarded as controlling the present.” (It is also used as a legal term with the same basic meaning.

~ James Alexander Thom