It is no accident that King's "I Have A Dream" is the one which shaped his posthumous public image. It is certainly his best known, and that is not an accident, either.
In April, 1967, King announced he was expanding his civil rights work to include the injustices he recognized as being immanent in the already fearsome, and always expanding, bloody intervention by the USofA into the civil war between North and South Vietnam. I have heard it was this sermon that got him killed. King was NOT talking to the black population alone; but his gravitas there might well have poisoned them to the injustice of the 'war' and deprived it of necessary cannon fodder, and was thus not allowed to long persist. The date of this sermon is April 30, 1967. He was assassinated April 4, 1968, while leading resistance in a labor dispute in Memphis. The man walked it.
Btw: Driftglass had this vid today. The comments there got me thinking. He's got a kewl site.