Fifty years ago today — and one year to the day before his assassination — the Rev. Dr. Martin Luther King Jr. delivered the most politically charged speech of his life at Riverside Church in Upper Manhattan. It was a blistering attack on the government’s conduct of the Vietnam War that, among other things, compared American tactics to those of the Nazis during World War II.

The speech drew widespread condemnation from across the political spectrum, including from this newspaper. Other civil rights leaders, who supported the war and sought to retain President Lyndon B. Johnson as a political ally, distanced themselves from Dr. King.

Dr. King’s Riverside Church address exemplified how, throughout his final 18 months of life, he repeatedly rejected the sunny optimism of his 1963 “I Have a Dream” speech and instead mourned how that dream had “turned into a nightmare.” But the speech also highlighted how for Dr. King, civil rights was never a discrete problem in American society, and that racism went hand in hand with the fellow evils of poverty and militarism that kept the country from living up to its ideals. Beyond signaling his growing radicalism, the Riverside speech reflected Dr. King’s increasing political courage — and shows why, half a century later, he remains a pivotal figure in American history.

As early as the first months of 1965, even before Johnson had begun his troop buildup in Vietnam, Dr. King was calling for a negotiated settlement to the conflict, telling journalists, “I’m much more than a civil-rights leader.” But his criticism of the government’s refusal to halt widespread aerial bombing and pursue peace talks attracted little public comment until that fall, when Senator Thomas Dodd of Connecticut, a close ally of Johnson, attacked Dr. King and cited an obscure 1799 criminal statute, the Logan Act, that prohibited private citizens from interacting with foreign governments.