Othello was a black man who married a white woman named Desdemona.
Since Othello was black, it was uncommon for people like him to marry a white woman.
Iago and Rodriego said racial slurs such as "thick lips" and "black ram" while he dated a white woman.
Othello wasn't just a black man, he was black man with power because he was a general.
Othello was an honest and true man so even the duke was on his side whatever problems he occurs in, and that makes white men hate him more as Iago.
Iago also gained power from getting Cassio fired and has taken his position until later on his plan is exposed and he loses dignity. He also tries getting power over Othello and does just that by manipulating him.