What circumstance or event is Dr. Martin Luther King Jr. , responding to in this letter?

Martin Luther King Jr. uses the letters to defends his strategy of nonviolent resistance to racism and opression. Some white clergy had recently criticized King's tactics in Birmingham. He states that people have the moral responsibility to break unjust laws in a peaceful manner.

He was responding to critics of the clergymen that his non violent actions were unwise and untimely.