Final answer:
The 'Letter from Birmingham Jail' by Martin Luther King Jr. was a response to 'A Call for Unity' that defended nonviolent civil rights tactics and criticized the white moderate and church leadership for their passive stances on racial justice issues.
Step-by-step explanation:
The letter that was written in response to 'A Call for Unity' by eight white clergymen is the famous 'Letter from Birmingham Jail', penned by Martin Luther King Jr. on April 16, 1963. Dr. King's letter was a profound defense of the strategy of nonviolent resistance to racism and condemned the white moderate, who is more devoted to 'order' than to justice. He expressed disappointment in the white church and its leadership for being an obstacle rather than a support in the struggle for racial equality.
The civil rights tactics which raised objections from the white clergymen included peaceful protests, sit-ins, and marches—all designed to challenge the segregationist status quo and to bring national attention to the injustices suffered by African Americans in the South. King addressed in his letter that the injustices in Birmingham and the urgency of the situation negated the calls for patience and slow change preferred by the white moderate clergy.