By far the largest Mermaid nation, the Intersea Coalition is one of the great powers of the Playground, on common rankings it places either between Extra Kingdom and Frostland, or tied with Extra Kingdom, easily a superpower. While it may sound like an international coalition, it really functions more like a confederation of semiautonomous states with a single government above them.
This one entity controls nearly 64% of the Playground's oceans and seas, they have nearly 45% of the entire Mermaid population.
For a reason most people cannot understand, they chose not to join the PCA, despite most of the states within wanting the IC to join. They often stay out of land politics, and advocate for complete separation of Mermaids and Land Peoples, an opinion most states within the IC do not support, and an opinion most non IC mermaid nations also do not support.
If it sounds like the Intersea Coalition government is not popular with IC states, you would be right, they have been on a decline as the confederal government keeps growing distant from its states and has already lost 3, The Bay of Pool Republic, The South Bay of Pool Republic, and the Shielded Gulf. Despite this, they are still an absolute powerhouse, and its states are pushing for reforms.