Let's imagine this.
Peaceful music plays as you walk down the streets of Afganistan. Then suddenly music changes to a more alerted tone , warning you that an enemy is within 32 bricks of your vicinity (or he's far away and you spotted him). And when an enemy jumps into your view, the music changes into brutal/heavy/intense/action mode (provided he's within the radius) as you and your enemy exchange bullets. After a few seconds of your enemy dying, the music changes back into relaxation. Or, if it's you who got mutilated, the music becomes sad/morbid/both until you respawn, or the minigame resets. Then music is back to peaceful.
Could go with 2D music events.