More than half a century after the Rev. Martin Luther King Jr. was murdered in Memphis, much has changed in America. Yet much remains the same.

One obvious example is gun violence: frequent in both eras, but different in kind.

In the 1960’s, the mass shootings so numerous today were rare. But assassinations of prominent leaders — notably those of King and of both John and Robert Kennedy — were all too common.

Similarly, consider race relations.

There is no shortage of racial hatred and injustice in 21st Century America; witness the revival of white nationalism and fears (or hopes), in some fraught circles, that a second civil war could erupt.

But thus far, our time hardly compares to the Jim Crow era of state-enforced segregation, police brutality, denial of voting rights, lynchings and the constant threat of arrest faced by King, other civil rights leaders and their many followers. King himself was arrested 29 times.

It’s difficult to imagine the kind of mass, non-violent protest movement led by King, which drew such fierce and violent opposition, arising in today’s America — although certainly the fight for gender and LGBTQ equality, exemplified by the 2017 Women’s March on Washington, is comparable in scope.

Immigration has come and gone as a major issue for this country for two centuries; in King’s time it was pushed to the background, while in our own it has been thrust forward once again.

In the 1960’s, the Cold War between the United States and the Soviet Union dominated international affairs, and American officials like the FBI’s J. Edgar Hoover were on ceaseless alert for those — like King — they believed to be communist sympathizers. Robert Kennedy, then attorney general, authorized Hoover to tap King’s telephone line.

Today, communism has been relegated to the “dustbin of history” — only to be replaced by the threat of radical Islamists like those who carried out the 9/11 attacks of 2001 and their many successors.

In the 1960s and into the ‘70s, beset by the war in Vietnam, America began to rend itself apart: war-supporting conservatives, particularly in the midlands, drew away from coastal liberals and young hippies, with their anti-war “peace and love” dreams.

Today that ideological disunion is complete: conservatives are triumphant with the rise of Donald Trump to the presidency; progressives are determined to restore dignity and constitutional legitimacy to the White House.

So it must be asked: can the American people peacefully heal the fractures and make our States once again stand United?