There's a difference between nostalgia and sober reflection. The arrival of 2018 will bring an unusually powerful cocktail of both: It marks a half-century since 1968, one of the most consequential, dramatic years in American life.

No single event will drive the commemoration, such as Pearl Harbor in 1941 or 9/11 in 2001. What made 1968 significant was its nonstop, extraordinary tumult that resonates to this day — a riot of struggle and doubt, of assassination and rebellion, of outrage and paradox: During that year's Summer Olympics in Mexico City, two black medalists defiantly raised their fists during America's national anthem to protest racial discrimination. Six weeks later, an episode of "Star Trek" seductively united Lt. Uhura (Robbins, Ill., native Nichelle Nichols) and Capt. Kirk (William Shatner) in TV's first interracial kiss.

Don't take enormous meaning from that juxtaposition; these were two of many random data points in what's often called the year that changed everything. America's most violent year domestically since the Civil War also saw Boeing launch the humped 747 jumbo jet and NASA launch the first humans to orbit the moon. And don't forget the bombastic politics and protests of the Democratic National Convention in Chicago.

During one 10-week percussion:

Lyndon Johnson, fearful that the divisive Vietnam War would cost him the looming Wisconsin primary, unexpectedly declared that he wouldn't seek another term. Later he would bitterly say he had dreamed he was being stampeded from all sides by "the rioting blacks, demonstrating students, marching welfare mothers, squawking professors and hysterical reporters." Worse, with Robert Kennedy maneuvering to revive Camelot, "the American people, swayed by the magic of his name, were dancing in the streets."

From a bathroom window at the Memphis rooming house across from the Rev. Martin Luther King's motel, an escaped convict fired one shot from a .30-06 hunting rifle. In that era of slower news technology, it fell to Kennedy to tell a supportive, mostly black crowd in inner-city Indianapolis: "I have bad news for you, for all our fellow citizens, and people who love peace all over the world ... Martin Luther King was shot and killed tonight." Kennedy implored his devastated listeners to pray for King's family and for America: "Let us dedicate ourselves to what the Greeks wrote so many years ago — to tame the savageness of man and to make gentle the life of this world."

Kennedy's campaign discreetly had King's body flown home to Atlanta. Soon, though, on the night Kennedy won the California primary, an assassin furious over Kennedy's support for Israel struck him with three bullets from a .22-caliber revolver in a Los Angeles hotel. Twenty-six hours later, Kennedy died.

Chicago, watching from afar, knew that discord stoked by war and rebellion would hit the city with tornadic force. City officials didn't know what to make of yippies' outrageous or maybe just outlandish threats — to kidnap delegates, to poison food, to torch explosions in storm sewers — but as city Corporation Counsel Richard Elrod later would reflect, "If you wrote it all off, you'd be remiss. When you have blowhards like (Jerry) Rubin and (Abbie) Hoffman, who can tell what's truth and fiction? So we determined to have a show of strength." The whole world watched protesters and police. Astonishingly, nobody fired a shot, nobody died.

Expect 2018 to be a history channel, a rush of reminders, replays and relivings, some of them resonant today:

A liberal movement in Czechoslovakia challenges Soviet hegemony in Eastern Europe.

North Korea seizes a U.S. Navy intelligence ship and, at a news conference, forces crew members to applaud their captors for treating them well.

North Vietnam's bold Tet Offensive against 36 locales in South Vietnam startles Americans there and energizes war opponents at home.

April alone delivers pathbreaking debuts of "2001: A Space Odyssey," "Planet of the Apes" and "Hair."

Rioting students and striking workers have French officials so fearful of civil war or revolution that President Charles de Gaulle briefly flees to Germany.

A sympathetic New York Post reporter writes, engagingly but apocryphally, that feminist demonstrators burned their bras outside the Miss America Pageant on the Atlantic City boardwalk; in fact the protesters had tossed symbols of oppression — girdles, steno pads, stilettos and, yes, unburnt bras — into a "freedom trash can."

All this and more from 1968 you'll encounter in 2018. Oh — and Richard Nixon defeated Hubert Humphrey and George Wallace to win the presidency. But that's a saga for another year.

— Chicago Tribune