I've outlined my story by writing down major events. Right now, an entire country gets invaded in 497 AD and the next action is in 500 when another country has a civil war. The problem is, nothing interesting happens between these. And since it's the early dark ages, there's not a whole lot of ways to pass the time I can think of. (As this is historical fiction, I'm bound to history).
The problem is the main event is in 500, until then there's not that much incentive for a civil war. Basically, the country has been electing a king for a while now, after a series of ones they had to depose. The current king decides to overstay his welcome by refusing to step down, so war breaks out.
Why not end one chapter in 497 and then start the next in 500? You don't need to write about the intervening years if nothing much relevant happens during them.
If you use a character to bridge the gap, that might work, assuming of course that you've got a POV character who is present at the final 497 event and the first 500 event. If not, if the first part is long enough to be a Part I thing, then the events starting in 500 A.D. (or whatever it's called now) can be the beginning of Part II.
Why did the king overstay his welcome? I'd suggest that the three years from 497 to 500 are filled with him doing unpleasant things that get on people's wicks, to the extent that they eventually decide to get rid of him (similar to what happened to Tostig Godwinsson in 1065 - for an idea of the unpleasant things he could do) Incidentally, if the country has been electing a king, that sounds a bit more like electing a president?
Not if: 1) Not everybody can vote 2) The only candidates available are all from the same Family and/or 3) The King has absolute power once he is elected
You could write it like Brandon Sanderson does with his Stormlight Archive. There's a six-year gap between the initial incident and the main story, but he leaps back in the timeline throughout the story to give the readers more perspective on the events that shaped the "present" story line. I just started the second book in this series, and if it weren't for those sort of flashback chapters, I definitely wouldn't be as head-over-heels as I am for Kaladin, that's for sure.
Why not introduce a storyline to run alongside the historical fiction. A love story maybe or some sort of brother vs brother entanglement. Anything really that can run side by side with the historical stuff and fill your 3yr gap.
If nothing important happens in the years between then don't write about them at all. Nothing wrong with skipping them entirely. Although, if they are based on actual events from history, it might be more interesting to speculate what might have happened in the years between. How close did things come to going an entirely different way?
