It wasn't just Saruman that brought about the enmity between the two races/cultures... The wounds go back hundreds of years, right to the inception of the country of Rohan. To the Dunlendings, the Rohirrim were always the invaders of the north, usurpers and upstarts. I too pity the Dunlendings, especially the way they were manipulated.
(Don't you just love bringing out these old threads, especially the ones that didn't get much attention at the time, really interesting.

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