Following the Night of Black Clouds, the giants waged war against the dragons. Every race was affected by the night to some extent, but the giants and the nomai were the only ones that could stand a chance in a war against the dragons, and the remaining Nomai/metallic dragons had been ordered by Bahamut not to take revenge.
The King of the Giants was called Odin. Prior to 700AD, he was an incredibly progressive king. The giants and dragons had always been at odds with each other, with a cycle of endless violence perpetuaded by each generation. Odin however, sought to end this cycle of violence, by no longer feuding with the dragons.
Before 700AD, the dragons had been helping the giants, but they were one of the few dragons who didn’t reveal their identity at any point during the help, due to the history of violence between the groups. The dragon actually married Odin, and they were expecting a child in a few months. However, when his wife and child were slaughtered alongside his people on the night of black clouds, Odin’s belief changed
“At the route of all suffering, is pain”. This is a roughly translated giant phrase. The rage Odin felt didn’t change his priorities – he never became some bloodthirsty mad man who suddenly enjoyed slaughtering dragons for revenge. Instead, his grief made it impossible to focus on anything but what the dragons had done to him, despite his kindness. He still prioritised ending the cycle of violence, not just getting revenge. Except now he believed that the only way to end the cycle of violence, was the complete genocide of all dragons and dragon born.
The other races supported the war with supplies and information, not being able to fight.