4 ideas
Captain van Toch, a Czech sea captain, finds intelligent newts in a lagoon at Tana Masa, an island off Sumatra. He trades them knives to fight off sharks in exchange for pearls, and he ships them to new pearl beds. The Czech industrialist G. H. Bondy turns this private arrangement into the Salamander Syndicate, which breeds and sells newts by the million as underwater labour for dams, harbours and new coastline.
Once a labour force becomes profitable, every firm and nation keeps supplying it with tools, explosives and weapons, each for its own competitive or military advantage. This continues even after the workers begin demolishing continents to extend their shallow-water habitat. The coordination failure is structural: no single seller can afford to stop, so humanity funds its own drowning.
The newts are discovered, not manufactured, but they are converted into a product through breeding, pricing, training and legal classification. Public debates about whether they have souls or rights serve mainly to justify their use. Status is assigned by economic function, so an intelligent species is treated as property as soon as it becomes cheap labour.
The victorious newts do not bring an alien culture. They absorb human technology, bureaucracy, mass education and expansionist 'living space' rhetoric, and the Chief Salamander turns out to be a human, a former First World War sergeant-major. The threat is humanity's own civilization copied and scaled up, so every nation reading the book sees its own conduct in the newts.