Today is a historical day. Monday won't make it into the history books, your kids won't be learning about last Wednesday and novels will not be written about two Thursdays ago. Today is a historical day.
That being said, let's examine historical fantasy and alternate history fiction.
Historical fantasy includes our own history with new elements of magic (consider Orscon Scott Card's Maker Series or Mercedes Lackey's Elemental Masters/Fairy Tale Series). Historical fantasy may be a retelling of known events with new characters or the presence of magic to explain certain events in our history.
The retelling of historical events with new outcomes (consider if the South had won the Civil War) would be considered alternate history fiction. If a minor incident occurs in the novel and has little to no affect on the rest of history, this would not be alternate history fiction. These novels have great changes, they leave echoes through time that would affect our lives no matter how many years after the event. Maybe that is a little dramatic, and they would only affect our lives if we lived in the book, but luckily we don't live in a book, or at least I don't have enough evidence yet to prove that we do...
How events are changed in the novel also determines if it's fantastical or alternate history fiction. If a character is propelled into the past (through science or magic) it would be considered fantasy or science fiction. If events are changed by the author with no new characters pulled out of time and place to be a catalyst for historical change, then the book would be considered alternate history fiction. Compare the book A Kid In King Arthur's Court and books by Harry Turtledove.
History is compelling. Changing history or explaining it in new light can make a beautifully rich novel. While we can often feel like life is passing us by and history is something to be bored with when sitting in a lecture or when your sister drags you to Gettysburg, PA to witness the land where so many brave soldiers gave up their lives in a futile fight to stay united! (or to stay free depending on what side you were on); history is happening, right now - today - this second. And even though I would love to take my time machine into the future and tell you how it all works out (everything, not just the election) my machine is temporarily out of service [insert funny anecdote here]; so we'll all have to watch history unfold, try not to be bored and continue reading unique historical works wishing we had been part of the past and never truly knowing how this moment affects our future.