Setting idea

>Have it so the tidal movements gradually increased over time

I assumed that the thing happened during centuries, and already said that you either use a lot of magic or science fiction.

The point of failure here is that there is no civilization to be had in the first point, because there is no way to start it; when the Tigris and Eufrates rivers were colonized they were a zone of stability with access to resources and water so people could band and organize together for around a thousand years.

And thats the starting point, bear in mind that "modern technology"(as arrows and really fine tools) happened around 10.000 years ago, so you need at the very least 10.000 years of stability and experimentation to have the foundation for a civilization.

And communication is essential, trading is what drives progress forward so unless you invent teleportation or give galleons to people right from the beginning they can only do island hoping, if there is no island or the distance is beyond acceptable terms you cannot compensate for your lack of specific resources or propel yourself into conquering other parts of the world and letting the most organized peoples to rule and expand their ideas.

But then, even with Galleons, with lets say 500 years of the sea reaching its lower level and 500 years of the sea reaching its higher level there are no forests to exploit(as already said, trees would have to adapt to conditions that change in extreme ways so forest can't regenerate easily) and life would be limited, this means that you can't create the richness, and without it there is no reason to have people administering huge amounts of resources, nor the means or motivations to use such resources into risky endeavors like exploration.
The zones that never get touched by the sea are the only ones that can have crops(the rest if pure salt), and those crops will suffer a lot when the sea has a regression and snow starts falling down, this also limits your population.

Or have the planet just be one planet in a larger civilization. Progress is imported as people move there.

You could just have plants and animals not be as we know them, it would be a lot more work than just handwaving it with magic or going sci-fi.
Underwater forests, lots of amphibious creatures, or even have it be an underwater campaign of seafolk or w/e.

Only rich kingdoms with brilliant minds could build an amphibious city.

A majority of the world would likely be nomadic, moving westward to run from the flood as long as possible, and then eastward into the flood to be done with it as soon as possible. Or vice versa for pirates and navies.

>they're spontaneous and random

That means they are cataclysms, so, you are literally telling people that in a few month or years they better start moving to higher parts and they don't know how much, if they do know how much then they will react accordingly.

Either way, the infrastructure will collapse, treasures will be eradicated, entire percentages of population will be lost, ecosystems will collapse in this time too and with them humans will suffer a lot too, and if the climate was just crazy before with constant cataclysms Neanderthal levels of extinction should be expected

>Some kind of magic could also be used to make plantlife

You solved a problem to add more, now you will have higher populations which means that you have one of the needed pillars for a civilization but such a population will face constant crisis every time the sea rises.

And lets not forget the impact of such a magic, according to the details of its inner workings you might end up with a society that is medieval in aesthetic and posthuman in its core. So if people is able to plant, lets say "sea water apple trees" through magic without limitations that means they have unlimited ammounts of wood and food, both of them results in a certain lack of trade, that is counterproductive into forming a civilization since there is no need for overcoming obstacles, but then make magic too focused on specific individuals and those individuals would actually behave like not like kings, but like tribe leaders, sometimes hindering progress sometimes making advances... that will be erased by the next tribe leader idiocy.

When you use magic the first complication you face is that magic, by its nature, even when limited is based around the idea that energy and matter are infinite and can be shaped by simple will which can easily turn into something like post scarcity societies.

I'm not saying that your setting is stupid, but it needs a lot of detail.

Could a small satellite around a massive planet have tides strong enough to pull entire oceans planet-side?

Or would such a system result in the satellite world being tidally locked (so that the same side of the small world faced the planet all the time and the ocean was just a stationary mountain of water)?

Or would tidal forces strong enough to pull water to one side also be so strong that anything within range to do this would be beyond the roche point and obliterated, forming a planetary ring?

I think before thinking of civilizations that would develop on such a world, I'd think that humans would probably not evolve on such a world. In fact, I don't think any large terrestrial creatures would evolve, it would all be small amphibious creatures that could tolerate extremes. Probably going into hibernation/pseudo-death during dry cycles and coming alive during wet cycles. There would probably also be no trees. Mining for minerals would also be pretty troublesome so I don't think metalworking would develop in any case.

So, to justify humans or any civilizations, you'd really have to import them from someplace (either magic or space travel), thus they would likely already come pre-civilized.

As already stated, all of that can be solved through a lot of magic or through science fiction, but I think OP is looking for medieval worlds that are constantly clicking the "new game" button with a random seed this time.

>Civilization can be preserved in this world. Sea-faring civilizations could just build Noah-style arks to house its population or just invade other islands á la Sea Peoples. A sufficiently advanced civilization could also build some kind of self-sufficient underground fortress to wait until the sea levels recede again and then swiflty take over all the land.

And I think he agrees with me in this point, either a lot magic or a lot of scientific handwavium can solve all of these problems, but then you wouldn't have a medieval society in the first place.

Another thing that should be accounted for is speciation, since it seems that most populations will end up isolated with giant seas from time to time, the parts that have the highest mountains where people can go back and survive will mean that the gene pool will be more limited and the evolutive pressure different region to region.

If the civilization evolved here, it would seem that it would be frozen in time for millions or hundred of thousand of years, so having 2 or 3 different species with social organization at the same time can and should actually happen, the only problem is making them contact each other in the first place.

For example: Neanderthals probably came from populations from H.heidelbergensis 600.000 years ago, and Neanderthals appeared around 200.000 years ago and we sure know that they had the capacity to be intelligent and form a civilization.

cont.

If in that space of 400.000 years they would have been left alone and your feudal empire contacts the other species, they would probably fuck up their development, and if it the other empire doesn't contact them in 400.000 years(without counting the supossed 200.000 aditional years to actually start a civilization) why would they do at any other point if they are frozen in time incapable of reaching them?

So to have them its a matter of doing it at the right time and moment but I do think its realistically very possible to have civilizations between people that can't hybridize or mix between them and would probably have real problems with communication too.(neanderthals did mix with H.sapiens but thats a story that goes beyond the point of this post)

Imagine a first contact with aliens but in medieval times, and similar or near level of technology(or maybe AztecsvsSpaniards all over again but with different species) which can be an interesting dynamic, the problem is making every part of if fit adequately.

>Would you play it?
If it was post apocalyptic or sci-fi, probably.

If it was fantasy, very likely not. As already pointed out in this thread, such a setting will require immense amounts of magic handwavium to work, and I really dislike fantasy settings like that. Not my cup of tea.

>Could a small satellite around a massive planet have tides strong enough to pull entire oceans planet-side?

Yes it can happen.

But think that if gravity is pulling the seas to over 100 meters, so does the crust and with the crust come earthquakes, volcanoes and all kinds of things that you would expect from something like "what would happen if we smashed Io against Europa?"

I don't know how it would affect the axis of the affected planet though, maybe it becomes so chaotic that now you have to add a planet that has a mad axis or one so fixed that follows the moon.

With tides that strong, it would definitely become tidally locked.

You wouldn't need magic for the plantlife. Plants are already seasonal. Rather than their seeds being carried on the wind, they could be carried with the tides. And there are species of real life plants that can handle both dry land and (shallow) water. Highlands would be green year round.

It's also possible that agriculture would be kickstarted. Being semi-nomadic, they'd have accidentally stumbled upon crop rotation, skipping a few thousand years of trial and error. Their crops would already be strictly adherent to the season. The plant knows its life cycle, so when the harvests are through and the plant starts dying, they know it's time to pack up and move on.

But even disregarding all that, unless you've got some players with agriculture doctorates in your group I doubt it would even be an issue.

What about if it was a binary satellite system, with 2 moons orbiting each other, orbiting the massive planet? Or would that system itself become tidally locked, with the two satellites sharing an orbit, rather than orbiting each other?

> Rather than their seeds being carried on the wind, they could be carried with the tides. And there are species of real life plants that can handle both dry land and (shallow) water. Highlands would be green year round.

Yes, there are halophyte plants that live near the sea but not hundred of meters under the sea.

And they would be kind of a bad idea to eat from one of them unless you don't like being isotonic from the rest of the world(I would imagine that people here must have giant and dense Kidneys, but I shouldn't expect to have a saltwater diet.

You could say that those plants have adapted fruit to have less salt, but then you run into an optimization problem; now the plant has to continually use energy to both fixate fructose and extract salt from the fruit(thats why you wont find that many trees in the coast too(and no, palm trees don't count as trees)

Also think that the plant has to adapt to three ambients, one that is constantly getting away from the sea in regression and one that will end up letting them up being engulfed in transgression(and thats supossing if the sea level is progressive, if its cataclysmic there won't be an adaptation, just spores or seeds) and one near the sea.

Most plants would be halophytes here anyway, since the land would be overloaded with salt that will concentrated when there is a regression and dissolved when there is a transgression, I would even say that finding plaster cristals and other evaporitic minerals should be very common.

But the point is, that I wouldn't expect those plants to serve for agriculture, and this world is too chaotic and changing; one day the tree is perfectly happy in their little zone salt overloaded zone fighting for being isotonic, the next day the sands carried from the winds start eroding the wood and killing the tree(its kind of spectacular though, the tree twists like is trying to dodge the wind is slow motion and then ends up falling with their cortex almost totally white)

>That means they are cataclysms

That is kind of the theme I'm going with this setting. Realms are created and destroyed in matter of generations, erased by the varocious sea. However, these perods of destruction are followed by eras of stabilization and reconstruction or even colonization of newly emerged lands.

> lets not forget the impact of such a magic

Maybe I have worded my post horribly bad, but what I meant was that plantlife could settle new lands faster and establish stable complex ecosystem in the matter of years, not that the civilizations in this world would have some kind of super-magic to grow food and wood at will.

>Another thing that should be accounted for is speciation

Not really, since the flood/drain cycle only lasts for a few generations at best, not enough time for speciation to happen. Seafaring cultures make this even more unlikely.
Absolutely right. I'm thinking that the inhabitants of this world were created directly by the gods of the land and taught the basic technologies to survive.

>That is kind of the theme I'm going with this setting. Realms are created and destroyed in matter of generations, erased by the varocious sea. However, these perods of destruction are followed by eras of stabilization and reconstruction or even colonization of newly emerged lands.
>As already stated, all of that can be solved through a lot of magic or through science fiction, but I think OP is looking for medieval worlds that are constantly clicking the "new game" button with a random seed this time.

So what I said here.

If you use the divine powers to handwave the civilization part, then prepare a lot of mythos since clearly gods there are interested in the lives of lesser beings and the civilizations are locked in progress, so thousands and thousands of years will pass and just by looking at all that happened in our 1000 years of medieval times the story of this world would be rich and filled with whatever the gods felt like adding at that moment.

Carefull with Gods too, they are a double edge sword, they can solve things since they are literall deus ex machinas, add plot hooks easily or being the main engine from the plot, but they have to be in concordance with the culture that gives them fidelity and the environment they live in, and creating harmony and coherence in societies is not easy nor something new, you would be writing about something that has been written since the start of times so originality is a bit hard and the temptation of simply mixing cultures and mythologies is very strong.

> that plantlife could settle new lands faster and establish stable complex ecosystem in the matter of years

Normally takes decades to see an obvious change in a ecosystem(at least the way I'm thinking you are referring to; instaforests), if it were to happen in 4 years you would be talking about trees that grow with insane speeds, this has implications too the difference is that we have something real to compare.

cont.

en.wikipedia.org/wiki/Bamboo
>Certain species of bamboo can grow 91 cm (3 ft) within a 24-hour period, at a rate of almost 4 cm (1.5 in) an hour (a growth around 1 mm every 90 seconds, or one inch every 40 minutes)

If they were to keep this growth(Bamboos as I can see are not trees but rather in the same family as wheat, so I don't know if its really constant or not and I don't have the time to delve into publications) 91 cm in 24 hours means that in 3 days the bamboo reaches nearly 3 meters, of course I can bet it doesn't actually do it but you get the idea. Bamboo grows insanely fast, and this has consequences.

Almost everywhere(and I say almost just in case there is some small part of the world that had it and didn't use it) in which bamboo grows people exploit it hard, since is versatile as fuck; you can eat it, you can use it to build houses and structures, clothing(although not all species), use it for fire, easy to grow(although only in their climate)... this meant that suddenly people could build homes easily and create infrastructure for irrigation and many things.

Now, I don't know if its directly related, but lets introduce the concept of a water empire. A water empire is an empire that bases its power on the administration of a single resource, the term comes from the Chinese empire where titanic amounts of water were needed for agriculture and only a strong bureaucratic empire could control and deliver the needed amounts, that meant that when one region was rebellious their water supply could be cut and if one region had problems and a history of rebellions its water supply was prioritized into other parts of the empire. These empires are so stable, that no matter how corrupt they get, they simply don't fall.

So by studying the chinese empire you can get a pretty good idea of how your idea of having supertrees would go, and Japan can teach you about a society that faces periodic catastrophes and has the supertrees too.

I don' follow your reasoning that fast-growing plantlife would result in a water empire.