Tolkien names the catastrophic battle that ended the First Age of Middle-earth the War of Wrath.
The War of Wrath was the final conflict of the wars against Morgoth, the first Dark Lord. It took place at the end of the First Age after the Valar answered the appeal of Eärendil. The Host of the Valar, aided by many Elves and Men, invaded Morgoth’s realm in the north-west of Middle-earth.
The fighting was so destructive that Beleriand was broken and largely submerged beneath the sea. Morgoth was defeated, captured, and cast out of the world. His defeat ended the First Age and permanently changed the geography of Middle-earth.
The War of Wrath is distinct from the Nirnaeth Arnoediad, the disastrous “Battle of Unnumbered Tears,” which occurred earlier in the First Age. It is also separate from the War of the Last Alliance, which belongs to the Second Age and concerns Sauron.