The History of Middle-earth \ Kings of Rohan Part II
“For two generations, during the coincidental conflict many thousands of Orcs tried to claim a refuge in the White Mountains and troubled the Rohirrim; Brytta fought them off, and when he died it was believed Rohan was free of Orcs; they were not entirely driven from the White Mountains until T.A. 2864 by Folca.
Around 2960 Saruman started to harass Rohan and in 3014, he began using his influence to weaken the King, Théoden, as part of a campaign to invade or take over the kingdom. In 3019, he launched a full-scale invasion of Rohan, with victories; (Théoden’s son, Théodred was killed during the First Battle of the Fords of Isen) and defeat at the Battle of the Hornburg, where the Huorns came to the aid of the Rohirrim. On the heels of this victory, Théoden rode with an army to Minas Tirith and helped break its siege in the Battle of the Pelennor Fields, where he was slain. Éomer, the nephew of King Théoden, then succeeded to the throne, beginning the third line.”