King wrote "Letter from Birmingham Jail" in response to what?

The Letter from Birmingham Jail, also known as the Letter from Birmingham City Jail and The Negro Is Your Brother, is an open letter written on April 16, 1963, by Martin Luther King Jr. The letter defends the strategy of nonviolent resistance to racism. It says that people have a moral responsibility to break unjust laws and to take direct action rather than waiting potentially forever for justice to come through the courts. Responding to being referred to as an "outsider," King writes, "Injustice anywhere is a threat to justice everywhere".