Vintage B movie with gory knife fight

This is a hazy recollection of a film I saw as a kid, which really shocked me. Trying to find out which film it was.

The premise involves a man re-uniting with an old friend who's become some kind of a hated gangster somewhere with a majority black population

(might be in the Caribbean or similar, not sure). 

Midway in the film there is a knife fight between a white guy and a black guy, where the black guy seems to be winning at first. At some point a broken bottle is used. The fight ends with the black guy on his knees covering his face, and the white guy slashing his hands with a knife, saying something like "Don't you ever try this again..."

In the end there is a confrontation and a fight between the protagonist and his old friend.

Any ideads which film this might be??