Chris Brown: It's War with Karrueche's Mgr ... He Broke Us Up!!

Chris Brown is still very bitter about his breakup with Karrueche Tran -- so much so, he's going to head-to-head with her manager Jacob York.

Brown started the beef when he saw a pic of one of Jacob's other clients wearing a Chris Brown tee. He reposted it with the caption, "@jacobyork fat ass is gonna have a speech for you" ... knowing Jacob's not a fan of his.

Jacob clapped back, "cocaine is a hell of a drug #davechappelle." Then Chris dropped a diss about Jacob's "commission money he get off da bitches he manage."

This has been simmering since Karrueche and Chris split -- a source close to Chris tells us CB thinks Jacob encouraged her to leave him. Of course, Jacob tells us that's absurd since Chris had a kid behind KT's back.He says, "I think [Chris] needs to keep me out of their personal life and take actions for what he did."

Karrueche finally sounded off too, saying to Chris ... "You're calling me a bitch but screaming my name in a song. Can all this petty s**t stop ... I'm so over the drama."

Guessing the answer is no ... it won't stop.