Social progress
Parker, Theodore. "Of Justice and the Conscience." Ten Sermons of Religion. Boston: Crosby, Nichols, and Company/New York: Charles S. Francis and Company, 1853.
Cooke, Sam. "A Change Is Gonna Come." Ain't That Good News. RCA Victor, 1964.
Douglass, Frederick. "West India Emancipation." 3 Aug. 1857, Canandaigua, NY, USA.
King, Martin Luther, Jr. "Letter from a Birmingham Jail." 16 Apr. 1963.
King, Martin Luther, Jr. "Letter from a Birmingham City Jail (1963)." A Testament of Hope: The Essential Writings and Speeches, edited by James M. Washington. HarperOne, 2003.
Quoting Martin Luther King, Jr., who likely was paraphrasing a quote by Theodore Parker in 1853.
King, Martin Luther, Jr. "Keep Moving From This Mountain." 25 Feb. 1965, Temple Israel of Hollywood, Los Angeles, CA, USA.
Vincent, Stan. "O-o-h Child." Performed by Five Stairsteps. Stairsteps. Buddah Records, 1970.
The Better Angels of Our Nature: Why Violence Has Declined
Pinker, Steven. The Better Angels of Our Nature: Why Violence Has Declined. Viking Books, 2011, preface.
Simmons, Lucille. "We Will Overcome." People's Songs Bulletin, 1947. Originally sung by Lucille Simmons and tobacco workers during a cigar workers strike. 1945, Charleston, SC, USA.
Marshall, Thurgood. "Fighting Back: 1957-1962." Eyes on the Prize, created by Henry Hampton, performances by Thurgood Marshall, season 1, episode 2, Blackside, 1987.
Berton, Pierre. The Smug Minority. McLelland & Stewart, 1968.