Geological / environmental event
Just as peace and prosperity had begun to take hold of Arleaon, a still-unexplained force sunders the world and joined it to another; one of fantastic flying ships and miraculous music boxes sending voices across the sea. "Like a mismatched holiday egg" a popular newspaper describes it. Most simply call it the Event.
"The day of horrors", as it is aptly summed up by one New York reporter, starts as a typical Monday afternoon and ends with two foreign armies facing each other down on an equally foreign landscape created from the merging of the City of Light and Three Kings. Fortunately cooler heads prevail and no great war results, though some skirmishes do occur along the Divide. Even with war averted, both cities suffer significant damage to infrastructure. Fires rage for days. Few cities are so directly impacted by the Event, but families and communities of all sizes across the globe suffer great loss. On the World of Magic side the loss of the southern Mountains means the greatest and most ancient Dwarven holds are gone, as well as the free dragonkin city of Tarsis. The World of Science is separated from Europe just as the entire continent is being pulled into war, not to mention the northeastern coast of the Americas and all of Canada.