Why the MLK anniversary matters in every city

MLK addresses a crowd at the March on Washington in 1963, where he gave the "I Have a Dream" speech. Photo: CNP / Getty Images

Fifty years ago Wednesday — on April 4, 1968 — a single bullet in Memphis, Tenn., changed the world: The Rev. Martin Luther King Jr. was assassinated.

Why it matters: Many of you weren't born then, and you'll hear a lot about this anniversary in the next few days. So I wanted to remind you what a transfixing, transformative event this was not just in the South, but for the whole country.