The Grand Reveal

Perhaps the most important date in humanities history.
On June 30th, 1866 dozens of events across the planet coincided together. Most famous of which, because it was the most noticeable, an explosion took place in the Tunguska region of eastern Siberia. It leveled miles of forest, flattening trees and cabins for miles in every direction. Due to the relative remoteness of the event's location, it was weeks before the cause became apparent.
President Lincoln of the United States, perhaps its greatest president since its first, is assassinated by John Wilkes Booth; a southern actor thrawled to an ancient vampire furious at the loss of her 'cattle'. At the same time, Indian rituals started to open tears between this world and the next, letting out a flood of spirits into many of the western territories.
John Dee, once a confidant of Queen Elizabeth I, revealed himself to the English crown. Providing many artifacts and manuscripts that would provide the basis for our understanding of the events that were going on around the world. 
The Black Forest, scene of and inspiration fairytales from the Brothers Grimm, lept away from its traditional borders. Swallowing most of southern Germany and spreading into France and southward in a single night, then it came to life. Thousands fled from its path, or resolved to hold out despite itself. It may have slowed to a relative crawl since it's first expansion, but the countries it invaded are still in a never-ending struggle to fight it back into check.
English explorers in Egypt broke their way into one of the great pyramids, awakening it's inhabitants. Instead of one of the greatest archeological finds of the century and beyond, they paid with their lives. They got off easy, as the surrounding villages soon had new, eternal, rulers to contend with. 
Looking back, it didn't take much for what we thought of as 'our world' to unravel completely, and the events listed are a small portion of what makes up the Grand Reveal.
And that was just one day.