Undead Disaster was a catastrophe in the New World that occurred over two hundred years ago prior to the start of the Overlord series.
Forty years ago, before Suzuki Satoru encountered Keno the entire Kingdom of Inveria had been turned into zombies. Unknown at the time this was the result of the machinations of the Elder Coffin Dragon Lord, who sought to strengthen itself to prepare against the next wave of players from YGGDRASIL created a spell that could absorb thousands of souls within a region.
The spell was not limited to Inveria. The zombie conversion had affected everything within 250 kilometers rendering three nations devoid of life. From a conclusion drawn by Suzuki Satoru’s, the event had led to the downfall of four nations.
The fate of these nations that were zombified had yet to spread to the other nations beyond 250 kilometers. It wasn’t until fifteen years after the event occurred did the neighboring nations began to notice. But by then swarms of undead spilling out of the affected regions and into neighboring lands.
A great deal of damage was done to the surrounding nations. And while some areas were not directly affected by it, many were people who lost family and friends. The surviving nations managed to quarantine the area infested by the undead leaving the areas a no man's land.