Conquest of the Green Shell astalakians

The city state of Oshamnus' first major conquest of a non-merfolk province was of the now defunct Greenshell Kingdom of astalakians. While the crab folk were called "Green Shells" they didn't have literal green shells. They did have a very rich quarries of virdilut so they were almost literally armed to the teeth in green colored armaments.   The Green Shell astalakian had superior weapons and fortifications. The Oshamnus had greater mobility and more combat veterans.   It was sort of an irresisitble force versus immovable object. The merfolk could not really breach most of the crab people's fortresses but the astalakians struggled to decisively defeat the fishtails in the open sea. There were lots of indeterminate skirmishes with mild losses.   A bitter stalemate went on for years before a cunning mermaid general was able to out maneuver the bulk of the Green Shell army with a series of feints and planned retreats to pull most of the astalakians out of positions allowing a second army to stage a sneak attack and lay siege to a number of under manned astalakian fortresses housing a majority of the hatchlings of the Green Shell leaders.   With their children as hostages, the astalakians sued for peace. The merfolk had won the war with relatively little actual blood shed.   The Green Shells expected that they would have to yield some or all of their virdilut quarries. The Oshamnus merfolk instead let them keep all of their territory and made the Green Shell king into an an Oshamnus governor. The Green Shell astalakians were allowed to manage their own affairs as long as they periodically supplied virdilut weapons, tools, and building supplies to the city of Oshamnus.