Kingdom of Hippogriffia/Marelantis
Hippogriffia is the ancient name of sea ponies that were invaded by the Storm King's forces around 970 C.S., and in an act of desperation, pleaded to the Old Gods for salvation, after pleas to Celestia went unanswered. Leviathan, King of the Ocean, answered these prayers, and transformed all of them into sea ponies (Hippocampus). They smuggled the Magical Pearl of True Form with them as they fled beneath the waves. Queen Novo, their ruler at the time (and who had, just the previous year, taken over for her mother), vowed allegiance to Leviathan for all time.
The undersea kingdom was named Marelantis, instead of the also-suggested Seaquestria, as Queen Novo took Celestia's lack of assistance as an insult. As was later discovered, her pleas to Celestia went unanswered as they were simply unheard. The Storm King made certain of it. In Earth terms, Marelantis and Hippogriffia are roughly analogous to Malta in size and culture. That is a Mediterranean (in this case, Mareterranian) culture, on a smallish island (and, in this case, an undersea city).
When NEIGHTO saw to the liberation of the above-sea island, and slayed the Storm King in 1005 C.S., Hippogriffia was re-established. However, not everyone wanted to rejoin the above sea lands and cultures. So, the Kingdom was divided, with those wishing to remain under the sea referred to as Marelanteans, and those above ground, Hippogriffians. For the time being, Queen Novo has vowed to rule over both kingdoms, though her intentiton is to split the two Kingdoms for cultural reasons after the war ends. With multiple daughters and both neices and nephews to pick from, the Royal Family has many options on who to hand over the dual crowns to. Like Equestria and many other nations, Hippogriffia/Marelantis has a Parliament, however, it's unicameral and more similar in size and scope to a city council, rather than a national government.
The newly freed nation of Hippogriffia/Marelantis had no industry, and its above-sea cities were largely in ruins. Vast subsidies of food, machinery, resources, and more were given by Prance, Rroam, and Vulpesylvania to help them rebuild as fast as possible, and sew good relations. Military forces were trained by the Vulpes, weapons were largely given by them as well, while aircraft were given by Roam, and warships given by Equestria. All in all, the newly freed nation found itself given everything they needed to start standing on their own four legs.
It's interesting to note that the Hippocampi that they were transformed into, were not the same as the true Sea Ponies of 10,000 years ago. Neither was their culture similar to theirs. While called "Sea Ponies" by some, their ocean-going forms technically are a different species altogether. All Hippogriffs retain the ability to transform back and forth into Hippocampus with the use of a piece of the Pearl of True Form. As these pieces are few, only select Hippus were given these, mainly for military purposes.
The Hippogriffs later created a special operations unit for undersea and littoral zone (sea shore) combat, the Royal Sea Air Land Service (Royal SeALS).
