The Sunder Isles were created over the decades after the appearance of the Dead God Fountain in 1510 DE. One legend says that powerful shock waves reverberated across the area, tearing the landmass into six large islands and hundreds of smaller ones.
After the Demon Spawn War (8972 GE - 9493 GE), a group of storm giants that had served under Thjorygg came to the Sunder Isles. They built homes along the cliffs and into the highlands of islands storm-wracked by the meeting of two seas. The currents of the area, along with its naval hazards, made it a highly defensible area.
In the 17th century of the Lith-Crillion Era, the isle's idyllic existence on a remote edge of the Brucrumus mainland, was broken. They became the target of raids by perhaps the most power-hungry of all the giantkind, the Eldritch. These were Thraedli raiders scouring the lands for weapons, lore and relics left behind from the wars. Wanting the storm giant's lore on controlling weather and handling lightning magic, along with their great wealth, the Thraedli warred with the people of Sunder Isles for decades. Matters were eventually settled when a high ranking Thraedli daughter was married to a highly respected storm giant captain. It allowed the transfer of knowledge without either side admitting defeat. Peace brought commerce, opening ports between the two sides, and an increasing number of Eldritch settling in the area. Most of these gave up their old ways of plunder, turning to farming and fishing, and learning the prayers of Thjorygg.