Military action
First global war that involved cities and nations across the globe.
It is believed that this war began as a confrontation between the Githyanki and the Goblinoids, that with prodding and clandestine actions of the Githzerai engulfed the world for a period of high level combat for about 3 years. Limited use of artifact weapons may have destroyed cities, but in the end there was a negotiated truce with all of the parties that held an uneasy peace for several decades. The Githzerai never declared war or signed the peace accords.