I have not read a single book by Amitav Ghosh (yet), but that should not prevent me from posting his opinion on writing historical fiction
Q: What sorts of things do you have to do to write successful historical fiction?
A: I don’t think there is any great difference between historical and other kinds of fiction. There are, in fact, very few novels that are not, in some sense, ‘historical’. Most novels are written in the past tense after all, and are based on the conceit that they are narrating events that have already happened. Melville’s Moby Dick was inspired by events that occurred decades before he started the book; the same is true of Tolstoy’s War and Peace. But today nobody thinks of these books as ‘historical novels’. What this tells us is that history provides novelists, poets and playwrights with different settings and situations: this does not mean that their themes are necessarily different from those that are explored by writers who choose to write about contemporary settings. In the end, novels are all the same in that they are about characters and their predicaments. Nobody would read a historical novel for the history alone. To be successful a historical novel, like any other, must have compelling characters.[Amitav Ghosh Returns to the Opium Trade in “River of Smoke”]