The War of the Thunder Lands occurred in the northern parts of Shardhelm. The 40 year war destroyed a large part of Mount Heragan in the HDP, shearing off a giant rock slab that lies still at the bottom of the icy depths, a home to many creatures of the deep, a massive reef, housing a leviathan that some of the residents worship, a peaceful dragon turtle that protects the reef from danger, and destroys any dangerous intruders.
Sharhelm was also very damaged, but from their own fault, they gathered their mages to create a spell to poison the lands for the dragons, and force them into extinction. Instead the spell decimated the lands and created countless magical abominations of the residents, and of the monsters that already roamed the lands.
The dragons were finally banished back from the Shardhelm and the HDP, when the metallic dragon King of good dragons, Bahamut, and the Chromatic 5 headed Evil queen of dragons Tiamat, fought. The battle of the Residents of Shardhelm, the HDP, and the king of Dragons vs Tiamat and her chromatic dragons, Decimated the lands, and created the flat areas of the Thunderlands that are still know today. The scars of battle in the north of Shardhelm still linger, the magics of the titanic dragons called Greatwyrms still scar the lands, residents of the Thunderlands have gained the abilities to breathe elements, some have grown wings, some even have gained scales that protect them from pain.