build is kind of ugly, transportation between islands is primitive and/or nonexistent.
would work much better if it was just one big island maybe with a mountain in the center, and the kingdoms surround the mountain on 4 sides, each kingdom equidistant to the next.
Edit: All of the mines could be connected in a system of tunnels and stuff that link all of the kingdom's mines together, all inside the mountain. Except make it like really forgetin confusing so people don't use the mines as a means of transportation, but instead use pathways through forests and stuff. Each faction could be in a different environment too, grassy, snowy, deserty, swampy...On top of the mountain you could have a really hard boss dragon or something that if you beat you get a stuff ton of plastic, would be near impossible to beat alone, so you could do it with people in your kingdom or other kingdoms could join together.
