The Dark Elf conflict is a conflict that lasted for thousands of years. Dating back to 2988 B.C.. The crisis was instigated when Malekith, the insane, genocidal leader of the Dark Elves, attempted to use the Infinity Stone known as the Aether, which controls reality, to eradicate the Nine Realms.
The Dark Elves were defeated and nearly exterminated by an opposing army of Asgardians led by the then-king Bor, and Malekith and several others of his species went into hibernation and until the next Convergence.
Result: Dark Elves are defeated. Most of Asgard's army is killed. The Aether is taken from the Dark Elves.