The idiom "make a full end" refers to causing his enemies to die. Alternate translation: "he will completely destroy his enemies" or "he will kill all his enemies" (See: [[rc://en/ta/man/jit/figs-idiom]])
Nahum speaks of Yahweh destroying his enemies in such a way that they will be powerless to avoid death as if Yahweh caused them to drown in a great flood of water. (See: [[rc://en/ta/man/jit/figs-metaphor]])
Here the word "darkness" represents the place of the dead, which is characterized as a dark place. Nahum speaks of Yahweh killing his enemies as if he were chasing them into this dark place. Alternate translation: "he will cause all his enemies to die" (See: [[rc://en/ta/man/jit/figs-metonymy]] and [[rc://en/ta/man/jit/figs-metaphor]])