The regions of the east that helped out Sauron were Numenorean colonies. The ruler of one of em became a Nazgul. The writing itself, due to not doing much physical descriptions, also avoids a lot of orientalist tropes that the movies go head on into, which could be influencing your view.

"It was Sam's first view of a battle of Men against Men, and he did not like it much. He was glad that he could not see the dead face. He wondered what the man's name was and where he came from; and if he was really evil of heart, or what lies or threats had led him on the long march from his home; and if he would not really rather have stayed there in peace - all in a flash of thought which was quickly driven from his mind" - Two Towes, Book 2, Chapter 4

[–] PolandIsAStateOfMind@lemmygrad.ml 7 points 3 weeks ago

The regions of the east that helped out Sauron were Numenorean colonies.

Umbar was, Khand was not but it was iirc ruled by nazgul, Easterlings and Haradrims actually had a very good reasons to ally with Sauron because every time Gondor had a good period, it invaded them. Also depictions of Haradrim iconography suggest it was just one faction out of that huge land.