The type of figurative language represented by the use of the word Selma in the provided stanza is allusion.
Allusion is a brief and indirect reference to a person, place, thing or idea of historical, cultural, literary or political significance, in this particular case the 1965 civil rights march from Selma, Alabama, in which nonviolent protestors were attacked by police. Allusions are just passing comments about which the writer expects the reader to possess enough knowledge to noticeits importance in a text.
The use of such figurative language affects the last line of this particular stanza by providung a description. Even though the descriptions referred to persons or things in allusions are not fully detailed, its use enables writers or poets to simplify complex ideas and emotions.
