Leo Tolstoy wrote in “Anna Karenina” that “All happy families are alike; each unhappy family is unhappy in its own way.”

Terror attacks are like unhappy families; each is different in its own awful way.

The unspeakable horror of 9/11 was a wake up call about how much some Muslims hate America and about the gaping holes in airport security and intelligence sharing.

Because another jihadist tried to ignite explosives in his shoe, passengers around the world must remove their shoes before boarding.

The Fort Hood slaughter taught officials to take signs of radicalism literally, even from those in the military, while the murderous rampage by a fiendish couple in San Bernardino spotlighted a program that admits foreign fiances without usual scrutiny.

The Boston Marathon bombing revealed the danger of something so innocuous as pressure cookers, and something so obvious as the need for the FBI to alert local police about residents pinpointed by intelligence.

From horrors in other nations, we’ve learned about the dangers of car and truck attacks, about airport terminal shootings and subway bombings.

The list of things we’ve learned in the last 16 bloody years is long but, as the slaughter in Las Vegas proved, not nearly complete.

It would be horror enough that Stephen Paddock carried out the most lethal mass shooting in modern American history under any circumstances. Yet the pain is compounded by how easily he circumvented all standard security measures, and the fact that investigators still don’t have a clue about why he did it.

As his brother said, the killer had no ideology, no religion, no politics.

That gaping hole, the x factor about why, is a bleeding wound in the American sense of security and safety. All the more so because investigators say he initially considered other attacks involving large crowds.

And yet nothing has publicly surfaced to place Paddock into any profile that would even make him suspicious. Although he bought a reported 33 guns in the last year, he passed every background check he was required to undergo.

He wasn’t a loner, but few people admit to having really known him, and none reported anything seriously amiss. So far there are no digital fingerprints or claims of allegiance to Al Qaeda or Islamic State, although the latter has claimed he was one of their converts.

It would be something of a relief if that claim were borne out. At least we would know why, and that would, in its own twisted way, be more satisfying than the maddening vacuum we face now.

The central mystery means we have entered a menacing new chapter of an already troubled age. The slow, steady progress we made in combatting terror, even from self-radicalized individuals, couldn’t save the 58 souls Paddock gunned down or protect the nearly 500 he wounded.

While all public venues have hardened their perimeters and internal security since 9/11, Paddock thwarted that simply by firing long-distance. He picked a hotel room with open views and was able to rain hell on the innocent at will.

Those bare facts mean our learning curve continues. At least some hotels likely will start screening baggage so that, hopefully, no other guest can casually take an arsenal and endless ammunition to a room.

In Washington, the move to curb bumper stocks and other devices that can turn semi-automatic weapons into virtual automatic ones is gaining steam.

These are all logical reactions, yet how does our society ultimately guard against an evil that has no logic? How do we combat an enemy so ordinary in appearance we can’t recognize it, an enemy that declares itself only at the moment it delivers death and destruction?

Tell me, how?

DeB Chris diss sowing hatred

It is a mark of Mayor de Blasio’s twisted politics that Columbus Day is now controversial and police protections are needed for Columbus statues.

Recall that the mayor jumped on the Confederate statue bandwagon by saying the city would search for its own “symbols of hate.” His continued refusal to exempt Columbus statues surely contributes to the spate of vandals defacing them.

Imagine four more years of his misrule, and all the things he could do to make New York worse. Then vote.

HS death ‘trap

Educrat nonsense of the week.

According to The Post, parents trying to get their kids out of a Bronx high school where one student murdered another face a rule that says transfers will be granted “where it is determined that the student’s continued presence …is unsafe for the student.”

In plain English, unless your kid is personally threatened, forget about it.

Hard ‘Times’ for creepy Harvey Weinstein

Harvey Weinstein now knows what it’s like to be a conservative in the crosshairs of The New York Times. The paper’s bombshell report was the opening salvo in a campaign not only to expose Weinstein’s years of depraved behavior toward women, but also to make him toxic in his profession and among the politicians he supported.

From the front page to the opinion pages, the assault is relentless. To my pleasant surprise, the Gray Lady is not letting its own liberal politics skew its coverage of a corrupt fellow traveler.

As for the defendant, Weinstein seemingly admits sexual misbehavior while simultaneously denying responsibility. His statement in response is a succinct example of everything wrong with modern liberalism.

He alternates between quivering and conniving, invokes Jay Z, references his mother and Bar Mitzvah, and ends by vowing to bring down President Trump and the National Rifle Association.

What sounds like a smorgasbord of raw emotions is a calculated reminder that he’s a longtime lefty who should get a pass. Besides, the sordid mess is not his fault.

“I came of age in the ’60s and ’70s, when all the rules about behavior and workplaces were different,” he writes. He admits to “my demons,” but has hired a lawyer to “tutor” him and “I’ve brought on therapists.”

He insists he’s remorseful, wants to apologize and knows he has to change — so now he’s going to “channel my anger” by attacking Trump and the NRA.

To its credit, the Times doesn’t let him get away with the song and dance. A stinging editorial calls on Democrats who took his contributions, including the Obamas and the Clintons, to condemn him.

“If such powerful leaders take the money and stay mum, who will speak for women like Mr. Weinstein’s accusers?” the editorial wonders.

Even more extraordinary, when Weinstein’s “tutor” said he denied some specific allegations, the Times called his bluff. A spokeswoman for the paper urged him to release all women involved from nondisclosure agreements, saying, “As a supporter of women, he must support their right to speak openly about these issues of gender and power.”

Dirty Harvey should take a hint. It’s time to roll the credits, his show is over.