Theolisian marshfolk

Prior to the draining of the Theolisian marshes, the marshfolk did not have a collective identity, instead living in semi-isolated villages comprising a handful of families. With the exception of fisherfolk and traders, the majority of the marshfolk never travelled more than half a day from home. Feuds between villages were semi-regular, though mostly took the form of raids on an enemy's fish- or eel-traps, and almost never moved into the realm of inter-personmal violence.
When the canal-cutters and mud-draggers arrived, and the drainage began in earnest, little consideration was paid to the marshfolk except demands for rent (a concept entirely alien to the marshlanders).
As the works continued, the marshlanders fell into two irreconcilable camps: those who were willing to adapt to the encroachment of the "incomer tide" and those who were not. The marshlanders who refused to pay rent on land they had worked for generations found themselves expelled and replaced by inlanders who would. Homes, boats, and traps were destroyed, and wildfowl were displaced by the drainage. As the incomer tide swept towards the sea, the marshlanders moved with it, dicovering a new identity defined in opposition to the inlanders.
True to their roots, the marshlanders rallied around a number of local leaders, but loss of land and food, new diseases brought by the incomers (in addition to the agues indigenous the marsh), and infighting between factions undermined their ability to resist, and the drainage continued to drive the marshfolk towards the sea.
The incomer tide finally stopped as the value of the land ran out - the marshes at the tip of the Sivikat peninsula flood too regularly and and subject to too many storms to make good arable land, so were kept as a stormbreak, protecting the reclaimed inland. However, the marshlanders had already taken to the sea, becoming the pirates, smugglers, and wreckers that plague the coast. The ones who remained on the land, both those who paid their land-tithes and those who kept to the marsh, turned their resentment inland, become brigands, poachers, and occassional saboteurs.