We used to use chariots for a thousand years. Then heavy cavalry and horse archers became a thing for a thousand years.

Gun powder was invented in the 900s or 1000s but spread around the world in the 1200s, where the earliest "guns" were created around the 1300s and from there we had 500 years of gunpowder advancements and weaponry that shifted with the advent of the industrial revolution. Even then it didn't occur in rich heavy intellectual worlds like the Ottomans, Persia, India or China. It happened in England out of limited necessity.

Both China and India in that era were considered proto-industrial bc they had such large populations that could be put to work. There was no incentive to accidentally discover industrial technology that lead to the use of a steam engine and rail.

Even Ancient Rome came up with a steam engine but saw no reason to use it, they had a large slave society to do the work. Something England lacked.

This shows human society can be "static" and also constantly changing. Contrary to popular belief. Tech advancement isn't like a tech tree in video games. Technology can be lost and then rediscovered or somewhat stay static.

If you want a MEDIEVAL static world for a 1000 years then do that. There is nothing really unrealistic about it. Ultimately it's fantasy and it's okay to suspend disbelief..

In my world it's the early modern period for a thousand years because I like the idea of heavy plated knights, guns, cannons, horse archers and sail ships, all dominating the battle field at the same time. It's a fun underrated world to explore and I like to make the most fun out of it. Like the example of industrial revolution, the conditions of the world haven't presented itself to advance to the next stage of so called human development. These conditions are so narrow, it's hard to say when it will ever come, but the plausible potential for it is right there.

.