To conquer a nation, rob it of its history and heroes.

That’s a quick summary of Marxist strategy, and it’s exactly what the American left has been up to.

President Donald Trump used the 250th celebration of our nation’s founding to warn of Marxists’ efforts to cancel our heroic Founders and erode our longstanding values.

“You can be loyal to Karl Marx or you can be loyal to America. You can be a communist or you can be a patriot. You can’t be both,” he declared at Mount Rushmore on Friday.  

The gravest danger America faces today isn’t a foreign power or a global pandemic: It’s the ideological takeover of our young people’s minds through our educational and cultural institutions. 

This Independence Day was a call to action in the war against that threat.

It was an opportunity to tell America’s amazing story so that younger generations embrace the values that made this country free and prosperous: individualism and respect for property rights, not group grievances and utopian collectivism.

In communism, there are no heroes, only oppressors and oppressed — and when you strip a country of its heroic past, you limit its future aspirations.

Ordinary Americans get that.

Some governors don’t.  

When every state was invited to outfit a booth on the National Mall to celebrate its distinct contributions to America,10 governors — most suffering from Trump Derangement Syndrome — refused to participate.

They played right into the Marxist nihilists’ hands.

So undaunted patriots from these states traveled to Washington, DC, on their own dime — and filled the booths themselves, instead of letting them sit bare.  

Donna Festinger, a retired teacher from Greenfield, Mass., drove nine hours to distribute 300 miniature maple syrup bottles, donated by a bottler in Shelburne, and other Massachusetts products to fairgoers.

Seattle radio host Ari Hoffman flew to DC and stepped into the breach left by Washington state Gov. Bob Ferguson.

“He claimed they didn’t have a booth for budget reasons, but spent $5 million on trans surgeries for convicted felons,” Hoffman fumed, as he handed out American flags and pocket copies of the Constitution.

When Connecticut’s Gov. Ned Lamont announced his boycott, I printed up large portraits of favorite sons Roger Sherman, Oliver Ellsworth and William Samuel Johnson — all signers of the US Constitution — plus the celebrated Revolutionary War hero Nathan Hale.

I went to DC on July 3 and used Connecticut’s otherwise barren booth to tell their immortal stories.

The next day, state lawmakers Rob Sampson and Gale Mastrofrancesco greeted visitors to the booth.

All of us came to celebrate our nation’s heroes and our history, which the Marxists want to eviscerate.

They call themselves democratic socialists. 

“Doesn’t that sound pretty?” Trump asked last week. “They’re actually communists.”

Rep. Alexandra Ocasio-Cortez (D-NY) dodges it by falsely claiming, “How a person identifies in their economic view of the world is less important to people than if we’re making their groceries more affordable.”

Don’t buy that dangerous deception: Our nation’s prosperity hinges on perpetuating our values of free markets, individualism and property rights. 

Those values and affordability go hand in hand.

Average individual wealth in the US is eight times that of collectivist China, and four times the average wealth in the highly regulated economies of Western Europe.

But self-described democratic socialist candidates are scoring victories across the nation, and young voters are the most receptive.

A new Cato Institute survey found that a staggering 58% of Gen Z voters choose socialism over competing economic systems, with communism and capitalism vying for second place.

That’s a wake-up call.

The July 4 festivities were a start, but rooting out the far-left indoctrination that’s burrowed into our schools and culture will take more than a celebratory weekend.

On Monday, the White House blasted the Smithsonian’s National Museum of American History for “refusing to celebrate the Nation and its history,” instead telling a story of “regret, tragedy and shame.”

It’s demanding immediate reform of the Smithsonian’s biased representations.

Florida Gov. Ron DeSantis is launching a new History of Communism standard in Florida schools to teach students the “catastrophic failures and human suffering caused by communist regimes,” in the words of state education commissioner Anastios Kamoutsas, the grandson of refugees from  the Castro regime.

Those of us in blue states have little hope for a similar initiative, but we can take more control of what our children and grandchildren are reading.

When I was a kid, I spent hours at the local public library reading every biography of great Americans I could find, from Paul Revere to Clara Barton to Thomas Edison.

Biography teaches that individuals, not groups and classes, make history. Heroes inspire.

When kids go to college, it’s hard to avoid Marxist indoctrination.

Instead of laughing it off, set them straight about the brainwashing they’re getting — and what they have to learn from heroes like George Washington or Douglas MacArthur. 

America has a great story to tell. 

Tell it well and the Marxists will lose. 

Betsy McCaughey is a former lieutenant governor of New York.