I think I should give the reason for my being in Birmingham, since you have been influenced by the argument of “outsiders coming in.” . . . Several months ago our local affiliate here in Birmingham invited us to be on call to engage in a nonviolent direct action program if such were deemed necessary. We readily consented and when the hour came we lived up to our promises. So I am here, along with several members of my staff, because we were invited here. I am here because I have basic organizational ties here. –“Letter from Birmingham Jail,”
Martin Luther King Jr.

According to the letter, why was King in Birmingham?

He had decided on his own to run a protest.
He had been asked to help stage a protest.
He had lived in that city earlier in his life.
He was a member of that community.