Battle of Fornost
The Battle of Fornost was the battle that defeated Angmar.
While the battle was a success in that Angmar was defeated, it came too late for Gondor's sister-realm Arnor: the last remaining part of Arnor, Arthedain had been conquered a year prior in 1974, and the last King of Arnor Arvedui had drowned in the Icebay of Forochel.
The battle was named for Fornost the old capital of Arthedain, and was fought in the plains before the city. With Gondor came Men from Rhovanion, Elves from Lindon, and the remainder of the Dúnedain of Arnor (among them Aranarth the Crown-Prince of Arthedain), and, according to the Hobbits, a company of archers from the Shire.
Angmar rode west to meet the assault, and seeing this, the cavalry of Gondor under Eärnur rode north into the Hills of Evendim to wait in ambush. As the main army of Gondor met the enemy and the battle began, the cavalry of Gondor attacked Angmar in the rear. Realizing that his forces were destroyed completely, the Witch-king of Angmar fled away east. Eärnur rode after him, but his horse shied away. Then Glorfindel attacked, and the Witch-king fled east to escape Glorfindel's wrath, disappearing from the north.
Thus the north was freed from the evil of Angmar, but Arnor was no more: those that remained of its people became the Rangers of the North.