Our world is surrounded by a metaphysical barrier that separates us from other dimensions and the things which inhabit them. This barrier is made up of 7 layers, with the last one being the closest to our realm. An ancient deity that exists across multiple dimensions is prophesized to enter our world and conquer it. In order to accomplish this, he must pass through the six layers separating our dimensions from his. The final layer would collapse with his birth into the mortal realm as a human child. A cult devoted to this prophesy has been operating since the beginning of mankind's history to bring about this event.
Throughout our 10,000 year history on this planet, the cult influenced certain events at different points in various time periods, shaping world history and slowly breaking down the barrier layers. When the king was finally born, it sent a metaphysical "tear" through the final layer of our realm, causing a devastating calamity. This natural disaster was felt worldwide and resulted in the deaths of millions of people.
When I look through history, the deadliest natural disasters are region specific, them being earthquakes, floods, etc. What I am looking for is a natural disaster whose effects can be made manifest on a global scale. I don't want something apocalyptic or world-ending. Society should still be functional and carry on, with some places obviously more affected than others. Nevertheless, I want the death count to be staggeringly high enough and on a global scale so that most continents experience some part of it. My focus is on:
- What natural disaster would fit this bill
- Where should it begin on the planet in order to have the maximum impact
- What must happen in order for it to be started.
How can I make this work?