Let's say that a fantasy world has a race of "amphibious humans" (i.e. they can survive underwater for long periods but can't do so indefinitely).
1. How would their military look like?
2. How would their economy look like? What would it be based on? How about agriculture?
3 (would it affect their politics in any way?)
Google Bajau Laut
What their military looks like would depend entirely on what they're up against in this setting. I imagine if they fought underwater against people of their same species they'd be using weapons with two blades on a pivot, basically big scissors, but that's just me. Spears/tridents work too, I guess.
Their economy would probably be based on the same things as normal humans, considering you made a point to say they can't live underwater. They'd probably dive for pearls a lot more than normal humans. I don't imagine they'd farm kelp or anything like that, but maybe they'd raise aquatic cattle of some sort.
Their politics would be affected by their lack of borders. You don't need a good boat to cross the ocean if you can survive off seawater and don't run the risk of drowning.
>aquatic cattle
Manatees?
I used the word cattle, but I was thinking giant clams.
Could always do literal seacows.
Aquaculture is always a thing
Would you need it, though? There's regular agriculture, too.
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Diversified food sources means a better chance of staving off famine in case of a disaster like drought, locusts, or a crop blight.
Greco-Polynesians. Basically nothing changes.
The original "mermen" of D&D were basically humans with gills. In this setting they're raiders who take advantage of their amphibious nature.
>long periods
How long can they hold their breaths down there?
Eight hours with normal exertion of leisurely swimming around.
If they were unable to survive underwater indefinitely I think they would eventually spend most of their 'free' time out of water. They would live along the coast but it is just much easier to do what you need to do in order to survive when you are not fighting against the force of the water especially given the fact you have to have access to the surface to breath.
Think of them similar to cultures that developed on islands. Much of their resources could come from fishing and the seas but when you start to talk about raising livestock it would be much easier to do free ranging animals on land. You could fence in pastures without having to worry about housing them in three dimensions. I think their biggest benefits would be working for other races that lack their abilities. They would probably specialize in water salvage operations and could even have strike forces akin to the navy seals.
I have a setting where one of the powers is this. They were originally normal humans living on a chain of tropical islands, but were changed by a passing god looking for new followers (it kind of worked). Gave them neck gills and made their skin gray and smooth, almost like a dolphins, let them withstand high pressure and the cold. They're building an empire from salvaging the lost wealth off the ocean floor, from sunken ships and lost civilizations. They've also developed some method of making high quality rust proof steel underwater using lost magics and hold the secret to making underwater concrete.
They're one of the major trade powers, exporting tropical fruits, animals, ship building and metalwork.
Their military is armed with magic railguns that fire a 6 inch steel dart. It works underwater as well as above (the rest of the world is just starting to experiment with gunpowder).
Their government evolved from the old ways of tribal elders of each village gathering to decide the future to having a circle of elected officials that choose a central leader (The Emperor).
They're also very mindful about water pollution. Flushing a cities waste into the ocean is a good way to get hit with an artillery strike
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What if they do need to spend some time underwater each day, like many amphibians?
They'll do the exact same, but swim more.
Okay lets presume a couple things. These amphibious men are closer to frogs than to men, smooth and slimy skin protects them but needs to be kept wet for at least a couple hours a day. They are not sensitive to salt and can live near the ocean as well as rivers. Maybe there are subspecies. Perhaps they need to be in water to mate. Therefore they live around and near sources of water, there could be populations in marshes, around rivers and lakes, and on islands and archipelagos.
>1
spears are always popular, and work just as well underwater in water compared to the land. it seems likely that their military doctrine would be based on the mobility of being able to move quickly between islands or rivers or marshes. It is likely that what are obstacles to us are not obstacles to them. Swords and blunt instruments don't really work so well due to water resistance under water. Armor is likely to be minimal at best, though camouflage seems effective in some scenarios. Raiders and ambush tactics could be the general military engagement, though maybe they could have powerful and interesting ship technology. It's hard to sink a ship that's semi-submerged already for example.
>2
Traders, merchants, pirates if they live in rivers and deltas and islands. Their food sources could be as equally aquaculture and agriculture, though they would be likely to have affinity with things that already live in semi submerged areas. Water buffalo or maybe weird things like manatee or hippo, mussel farming is easy.
Controlling rivers and places of trade is huge in terms of economic potential.
>3
fuck yes it would. Location and economy impacts human politics in a huge way. I imagine the river mouth frogmen to be gregarious, likely to take in travelers (for a price) and xenophilic, but the marsh and isolated frogmen would be wary and hostile because of living in hostile environments.
They probably be like gillmen in pathfinder In terms of war, sneaking up on enemy ships and stabbing holes through it, then using sharks as cavalry
>These amphibious men are closer to frogs than to men
Whatever gave that impression? They're clearly more like discount Sea Elves.
because discount sea elves is shit and it's more interesting to me to have a springboard to work from like 'they have to spend a little time in the water each few hours'
if we're going with the OP picture fuck it then have them be island dwelling noble savages who are all super handsome and dive for pearls, picking seaweed and who have a king and stuff.
There's actually a lot of depth you could give to a Greco-Polynesian civilization to make it less "one dimensional noble savages", even just taking from those two cultures.
e.g. slavery, slavetaking and the slave trade, ritual cannibalism, reverence of oracles, observance of taboos, the erection of monuments, the education of the noble caste, etc.
Dolphin rape caves, all the time.