There's many ways to start a song. Just like a story, there's personal experience and allegory. Like poetry - there's words, meter, timing, dynamics and delivery; not to mention the choice of key and musical style.
I've been working on hate. Peering into myself and the surroundings. It's easy really, there's plenty of it and I'll admit that I'm prone to the dark side more than the light. It's also easy for me to see it in other people. That said, I looked into fratricide for inspiration and came up with some interesting comparisons. John Berryman drew from Shakespeare to create his 77 Dream Songs and His Toy, His Dream, His Rest. Shakespeare's Hamlet is Berryman's Henry. An argument go's like this: Hamlet kills his uncle Claudius because Claudius supposedly killed Hamlet Sr. to become king thus Hamlet's stepfather. Hamlet doesn't like the idea of his uncle (his fathers killer) becoming king much less sleeping in the same bed with his mother Gertrude. It's a familial killing and it's not a clear case because it's Shakespeare. Berryman brings it a notch further with the use of modern psychology. Berryman's Henry contains a double self. One self succumbs to the other through self hatred brought on by the suicide of his father and we're left feeling the loss of the weaker self. As one character triumphs over the other everything is lost. Shakespeare tells the story through multiple characters and Henry's fratricide is internal. Similarities arise in allegorical and modern times. Cain and Able for the god fearing, Romulus and Remus (Cassius/Brutus and Ceasar) for Rome and semite killing semite or Israeli killing Palestinian in todays world. Between the Jewish and Arab conflict we see another time honored tradition in familial killing - The Mark of Cain - meaning revenge is seven fold. If we are to follow this to possible outcomes we should wonder if Jews and Arabs in this part of the world might both loose to the another enemy, their Fortinbras.
My very small sketch of a song contemplates this by creating a musical equivalent with tension placed between Amaj and Abmaj. The horns play a G#(7th) and E(5th) movement to complete and compete with the Amaj and Abmaj chord voicings. An F6 is a half-step up from the flattened Amaj. making a movement in halfsteps or as I like to think, stepbrothers. The dissonance created by the horns, guitar and vocal is like an entire family killing itself. Like Hamlet. You can listen to the slaughter here