Near the 2000th year of the Third Age, the Wainrider people from the east made an alliance with the Haradrim, and a dual attack on Ithilien was launched. While the Wainriders assaulted Ithilien from the north, the armies of the Haradrim crossed the Poros and invaded South Ithilien.

The northern assault of the Wainriders was met by the King of Gondor himself, Ondoher, with his two sons Artamir and Faramir. The Easterlings swept through Gondor's defence, cutting down the King and his heirs and routing his army. Their victory complete, and Gondor defenceless before them, the Wainriders paused in North Ithilien to celebrate their conquest.

Their allies in the south had met with much less success. The Gondorian Captain Eärnil had led Gondor's inferior Southern Army to victory over the Haradrim, destroying their army in South Ithilien, to the north of the Poros. After his victory, Eärnil turned north.

The feasting Wainriders suddenly found their success reversed, as Eärnil appeared with his Southern Army, reinforced by fleeing members of Ondoher's defeated northern troops. Eärnil's army descended on the unprepared Wainriders, driving many of them into the swamplands of the Dead Marshes. That eastern people, for so long a dreaded enemy of Gondor, never marched against Gondor again. The battle was named after where it had taken place: the Battle of the Camp.

Because there was no heir apparent to the throne, Ondoher and his sons having been killed in the battle, Eärnil was made King. He was a distant relative of Ondoher, and could trace his lineage back to Elendil and Anarion of old.