The Battle of Fornost, fought in TA 1975, was the final battle of the Dúnedain and their allies against the forces of Angmar. The Battle came following the Fall of Fornost in TA 1974, when the land was overrun by the armies of Angmar.
The forces of Círdan of Lindon and Eärnur of Gondor, combined with the remnants of the people of Northern Dúnedain and forces from Rivendell (led by Glorfindel), were victorious in driving out the Witch-king, destroying his army as well as the power of Angmar. But the Witch-king was not physically defeated; Glorfindel prophesised that he would not die at the hand of a mortal Man (he would later be slain by Éowyn at the Battle of the Pelennor Fields during the War of the Ring).
Years later, when Eärnur became the King of Gondor, the Witch-king resurfaced and challenged him; Eärnur initially refused, but when the Witch-king challenged him again seven years later, he agreed. Eärnur rode into Minas Morgul, where he was taken by the Nazgûl and never heard from again; following his disappearance, the South Kingdom of Gondor did not have another king until after the War of the Ring.