At the time Araphant (Sindarin) inherited his kingdom from his father Araval, Arthedain was already in desperate straits. The Witch-king of Angmar had been beleaguering the northern lands for nearly five hundred years, and Arthedain's resistance was beginning to fail.
The one hope that Araphant had left was to renew the ancient bond with the South-kingdom of Gondor, which was at that time suffering losses itself at the hands of the Wainriders. He forged an alliance with King Ondoher of Gondor, and sealed it with the wedding of his son Arvedui to Ondoher's daughter Fíriel. Araphant's foresight failed to bring help to his kingdom, though, since Gondor itself was under sustained attack and could send no troops to his aid.
Four years after the alliance was made, Ondoher fell in battle with the Wainriders, and the South-kingdom was left Kingless. Araphant's heir Arvedui made a claim to the Kingship of Gondor, which would have reunited the two Kingdoms, but Steward Pelendur moved the Gondorians to reject it.