Wars don't just happen for no reason - what is the reason here? Are we talking about a full-scale war of conquest, where one nation believes the other is going to invade and take it over entirely? Or a limited war of conquest to take a smaller island or two with valuable mines/fisheries/agriculture? Or a war to secure trade routes and prevent trade by the other nation? Conquest requires troopships and enough warships to protect the troopships and provide indirect fire support. Convoy raiding/security requires U-boats and escorts. So, what is the mission of each nation's navy?

Your minor countries aren't going to be building navies themselves. Depending on their budgets, they're either commissioning new ships or buying older, slightly obsolete ships from the major shipbuilding powers. There were quite a few countries in South/Central America with similar populations around the time (look at the list linked by LDutch), with some digging you can find information about some of their navies which should give you some ideas.

@KerrAvon2055 The primary concern of these navies is a varies between full scale conquest and taking over portions of each other. Although only smaller scale skirmishes actually happen they are still worried about the potential of full scale war. I'll ad it to the body of the question.

@user111403 unlike most smaller nations around this period these island nations are actually about as industrialized as a country could be in this era. They're still limited by their size but the ones on the higher end 500-600k to one million mark do have moderately sized shipyards. Also most of those countries kind of just, don't have navies around this time because they don't expect to be fighting wars or expect to fight wars where they'd have no hope of mustering a navy comparable to their opponent.

@OT-64SKOT It's your story to write so your choice, but realistically, countries of that size are building too few warships for investing in the infrastructure to make economic sense. Economies of scale will apply, the major powers will produce warships both cheaper and faster. Even if your countries have the theoretical capability, they're still better off buying and using their industrial capabilities in other ways. In the real world a lot of smaller countries and even not so small like the Philippines use mostly imported equipment for these reasons.

@user111403 I guess that makes sense, although i was thinking that they would import things like guns and armour plate and build what they can in their own primarily civilian shipyards.

@OT-64SKOT I'd guess that might make sense a century earlier when (at least in my limited understanding) a naval ship might be just a civilian ship with a few more guns, but probably not by the time you're well into the ironclad era. Incidentally, there's pretty major development in naval technology over the period you've picked (ironclad->pre-dreadnought->dreadnought), although probably none of your countries are going to be operating dreadnoughts, some of the bigger ones might have a couple battlecruisers or armored cruisers. Your smaller ones are probably going to focus on torpedo boats.

As in RL, you first clarify which threats your pet nations face, what kinds of assets they can rely upon, and work from that.

The problem is that i really can't tell. They're fighting eachother. As countries like what i'm talking about didn't really exist in this period irl i don't really know what they've got or what they're fighting against because it's entirely hypothetical.

I dont think Island nations with that kind of economy cannot exist in a vaccum, either they will be much poorer, or have extensive trade networks that can potentially make them ludicrously rich. Think Dutch East India Company. Maybe thats what they are fighting about? That would also totally change the amount of resources they can throw at shipbuilding.

If 100k means 100 KM, and not 100,000, you should fix that. If it does mean 100,000, what is the unit of measure.

resources will be your biggest limitation, islands can vary a lot, do they access to iron, oil, timber ect?

@Xavon_Wrentaileit's i meant population, people

"They are willing to sink a large amount of their economy into constructions of their military". Not if they want to maintain their high per-capita GDP. See the Soviet Union, for example.

@RonJohn I more meant anglo-german naval arms race military spending not soviet leve spending

Do we have aircraft?

Isn't lumping together 100 thousand and one million people a lot of a stretch? All other things being equal, won't the big state more than happily kick the stuffing out of the little neighbour? 'Industrialized' or not, how could such tiny territories have GDPs per capita comparable to 'wealthier industrial European economies of the period'? Isn't 'their economies are obviously limited by their populations and land area' broadly similar to saying 'their economies can broadly not be comparable'? What, here, does 'industrialized' actually mean?

Can you please re-phrase 'Their major concerns are a mix wars aiming to take a limited amount of territory from others or complete conquest, although notably while some wars aiming to take pieces of territory occur no larger scale attempts at complete conquest actually happen but they continue to remain a concern' to make it (much) more clear?

When 'They have access to the full range of naval technology they can afford' how should anyone measure what they can afford?