how does Martin Luther King Jr., show grit in the " Letter from Birmingham Jail"?

Dr. King expands this context to suggest that the general consensus – that moderation is preferable to extremism – is false. Moderation, he argues, allows injustice to flourish while otherwise good people can comfort themselves with the belief that patience will solve society’s ills. The only way to truly enact change and help mankind transcend its limitations is to not only act with but also embrace extremism. Though he takes great pains to frame his movement as “creative” (rather than destructive) extremism, Dr. King firmly contends that one must be willing to actively pursue change lest he otherwise be accused of cowardice in the face of injustice (180). Despite its measured restraint, the “Letter” is an argument for taking action, and against hiding behind platitudes of moderation.

Thank you! And can you answer;

In what ways did African-Americans display grit during this time period?