Final answer:
King was arrested for parading without a permit during nonviolent demonstrations in Birmingham. He wrote 'Letter from a Birmingham Jail' in response to white clergymen's criticisms, defending the civil rights movement's tactics.
Step-by-step explanation:
Martin Luther King Jr. was arrested for parading without a permit during the Birmingham campaign of 1963. This was part of several days of demonstrations that he led, aimed at ending discriminatory practices and segregation in Birmingham, Alabama.
The peaceful protests were met with violence by police, and King, among others, was arrested and placed in solitary confinement. In response to an op-ed by eight white Alabama clergymen who called for patience and criticized the protests, King wrote his "Letter from a Birmingham Jail." In the letter, he defended the civil rights movement's use of nonviolent protest and civil disobedience and challenged the notion that African Americans should wait any longer for equal rights.