I like to personally consider U2's Sunday Bloody Sunday as a song that describes a kind of an awakening or a realization. The song describes from the vocal's perspective the killing that took place in Ireland. There are two Bloody Sundays in Irish history, one in 1920 where British soldiers fired at an Irish crowd. The second one took place on January 30, 1972, when 13 Irish citizens at a civil rights protest in Northern Ireland. Seeing from the time of U2's debut and the introduction of the song, it describes more of the second Bloody Sunday.
U2 emphasizes the political neutrality of the song and denies of it being related to any political opinions. This is why I think it represents a realization; the impartial song condemns any sort of bloodshed in general and cries for peace and nonviolence around the world. By announcing such bloodshed to the world in a from of a popular culture, he is sharing the mean nature of violence and is asking for change around the world.