The Pirate Coast (Swords & Wizardry) (2013)

From publisher blurb:

In ancient times the Pirate Coast was home to a great civilization of stone giants. The stone giants maintained a wide-reaching kingdom of towns and villages. Despite their great size and power they relied on slaves taken from the primitive human tribes of the coast. In time, the stone giants grew lazy and decadent, and when humanoids poured into the coastal lands and gradually destroyed the stone giant kingdom. The stone giants were more powerful than the humanoids, but they were more numerous and they outbred the giants. Worse yet, the stone giants found themselves plagued by slave revolts. The humans of the coast founded their own kingdom on the island to the east of the coast and came to be called the Bucranians by the bull skulls they used as standards. More than a century ago, the roving pirates of the White Island discovered the wealth of the Bucranians and began raiding their villages and towns. When the White Islands sank, many settled along the Pirate Coast and started making deeper and deeper raids into Bucrania, burning villages and carting away slaves from the old and lethargic kingdom.