it starts with Karnak, a simple man who's home was attack by the night haunt, and all thous specters where people he had known who were suffering for false crimes agents Nagash. Enrage by how he twisted death to his own purpose he swore to destroy him. The storm cast went there and he would come to see them as outnumbered and stretch to thin. So ensued of trying to join them he stared travailing the realms in search for knowledge or power, something that was overlooked. After looking for some time he came open an anthill, he them recall a time in his youth when he saw ants on a lion carcass. This gave him a revelation that with such numbers ant ant could fell a lion, so he would create a new race one with the forms of men, the strength of dragons and the numbers of ants. So he started experimenting using ant queens, human and dragons blood, and mostly the winds of beast and life and those he was successful with the birth of the first Myrmidon queen, he was corrupted by the magics of he was using and the nature of the ant queen, The need to feed and expand their brood. So he became a creature like his queen and they consummated the first brood. but the pure born children were flawed they were perfect killers and builders but they had no thought beyond what their queen or father gave them, but Karnak had a solution, useing crystals he found on his travels he found a processes were his queen could eat a person and their soul would then be bound to the hive and become the true born Myrmidon's and each time they died they would return to the queen and be born in a new body. In time Karnak would spread a queen to each realm, but ultimately he would fall to his instinct's and delusions of "saving" the people of the realms from Nagash. He is now Karnak The All Father and his Myrmidons as much a all consuming scourge as a grand civilization.
(this is roughly most of what i thought of but its probably to much but i could add more)