If you’re wondering how America and Western Europe went from marriage-centered societies to post-Christian sexual anarchy abetted by massive government growth enforced by brutal political correctness in just a few decades, let’s just say it was no accident.

Here’s a brief history:

The progressive left has been in a death struggle with religion, the family, capitalism and morality itself since becoming a political and philosophical force during the French Revolution.

With the advent of Marxism in the mid-19th century, the battle intensified, with the left eagerly expecting the collapse of capitalism.

When the West failed to succumb to an economic and political upheaval of the type that seized Russia in 1917, the strategy changed. To liberate people from free market capitalism, it became necessary to liberate people first from bourgeois morality.

Man’s natural inclination is to provide for himself and his own extended family, then for his neighbors and community. Socialism must remove existing loyalties and institutions in order to replace them with government power. That’s why progressives have been a major force behind abortion, easy divorce, single-parent welfare incentives, pornography, collective child-rearing and sexual excess of all kinds. All of these manifestations of the progressive disease weaken the natural family. As families crumble, the state steps in to take their place.

Italian communist Antonio Gramsci saw the value of this in the 1920s, calling for his fellow revolutionaries to “capture the culture,” that is, infiltrate the institutions that transmit cultural values. So they did, especially in the universities.

Revolutionaries such as John Dewey, Margaret Mead, Margaret Sanger, Herbert Marcuse and Wilhelm Reich, all of whom waxed poetically about the Soviet Union, inspired progressive educational and social policies that weakened support for organized religion, marital fidelity and the family while empowering the state.

With the help of like-minded people in Hollywood, they hammered away at social conventions of all kinds. The weapons of choice were radical individualism and moral relativism, which they peddled on college campuses to credulous liberal faculty who passed it on to their students.

By the time the 1960s rolled around, with the advent of the pill, Playboy magazine and mass communications, Western civilization was ripe for takeover by a heretofore alien, ideology of limitless sex. Of course, people weren’t told about the downside of “free love” — the destruction of families, social chaos, the loss of freedom to disagree, and a tightening statist grip on economic and intellectual liberty.

In his masterful new book, “Takedown: From Communists to Progressives, How the Left Has Sabotaged Family and Marriage,” author Paul Kengor traces a direct line from the founders of communism to today’s liberal social “reformers.”

The elements change with the times, but not the ultimate objective, which is to “progress” indefinitely toward an evolved, socialist Eden where all is shared and all are equal. Mr. Kengor notes that the progressive canon changes rapidly, and in ways that even progressives cannot always predict.

“But we do know this much: what is seemingly inconceivable to all of us right now, including to progressives themselves, may become the dogmatic position of progressives in a generation,” he writes.

For example, “just five years ago, Barack Obama and Hillary Clinton” supported “retaining the definition of marriage as between one man and one woman by 2012, that was completely gone. Now, anyone who opposed redefining marriage — and who stands now where virtually all Democrats stood a mere two decades back — is derided as a bigoted extremist.”

A case in point: The ninth World Congress of Families, which will be held this coming week in Salt Lake City, has drawn fire from the Southern Poverty Law Center, the Human Rights Campaign and other leftist organizations, which falsely and strategically portray the pro-family gathering as a “hate” event and the speakers as bigots. I have done some writing for the WCF, and will be on a panel about “How the Culture Undermines Life and the Family.”

In the Communist Manifesto, Karl Marx, who had an affair with his children’s nurse and mistreated his own family badly in other ways, railed against religion and the middle-class family: “The bourgeois family will vanish as a matter of course when its complement vanishes, and both will vanish with the vanishing of capital.”

His co-author, Frederic Engels, was a prolific philanderer who preached free love in an 1884 essay as a benefit of political revolution, a few decades before abortion became the holy sacrament of the political left:

“With the transfer of the means of production into common ownership, the single family ceases to be the economic unit of society. Private housekeeping is transformed into a social industry. The care and education of the children becomes a public affair; society looks after all children alike, whether they are legitimate or not. This removes all the anxiety about the ‘consequences’ … Will not that suffice to bring about the gradual growth of unconstrained sexual intercourse …?”

The progressives’ contempt for the family contrasts with the timeless definition of marriage given in Genesis 2:24 and reiterated by Jesus: “A man shall leave his father and his mother and hold fast to his wife, and they shall become one flesh.”

This article was originally posted at the WashingtonTimes.com.