So who is an American? What’s the key to American identity? The answer can be hard, even brutal. But it’s ours – we earned it with our own blood.

Whenever America travels around the world in a military adventure – or misadventure – the question needs to be answered anew. And whenever globalists and open-borderers want to bring the world here, without respect for American culture and tradition, that question needs to be answered yet again, even more emphatically.

The classic exposition of American identity came from a Frenchman-turned-American named Hector St. John De Crevecoeur. He moved here in 1754, and three decades later, in “Letters From an American Farmer,” he asked, “What then is the American, this new man?” And Crevecoeur answered, “He is an American who, leaving behind him all his ancient prejudices and manners, receives new ones from the new mode of life he has embraced, the new government he obeys, and the new rank he holds.” Crevecoeur concluded, using language anticipating the “melting pot” image of a later century, “Here individuals of all races are melted into a new race of man.” Yes, Americans can treasure their ancestry. But they must treasure even more their citizenship.

Americans gained a poignant reminder of their American-ness on 9/11, when the entire nation was under attack. We still cherish the unifying memory of that public service announcement immediately thereafter, in which Americans of all ethnicities looked at the camera and spoke the same words, in the same language, “I am an American.” It’s a beautiful sentiment, beautifully realized. And while it can be found on the Web at adcouncil.org, it should still be on TV.

Meanwhile, we are constantly reminded that American identity has been forged in fighting.

A new movie with a James Fenimore Cooper-ish title, “Pathfinder,” hits on these themes with the force of a broadsword – literally. Specifically, in its Hollywoody way, the film reinforces Crevecoeur’s point: When you become an American, you have a new identity and a new loyalty. And if necessary, you must fight against your old country, in defense of your new country.

That’s what happens in this film, set in America many centuries before Columbus. “Pathfinder” spins the yarn of a Viking orphan boy, saved from death by Indians, who raise him as one of their own.

Then comes the test, when another Viking marauder band arrives, bent on conquest. The boy, now a man, must fight with his new people against his old people.

The movie is not for everyone. It’s bloody – although, of course, American history has often been bloody. And yet, war has often been the crucible for nationhood. German-Americans, for example, felt twinges in two world wars, when America’s enemy was their former fatherland. Yet German-American warriors, notably Gen. John Pershing and Supreme Commander Dwight Eisenhower, oversaw Uncle Sam’s victory over the kaiser and Hitler. So the American vision – molding Crevecoeurian “new men” – was once again resoundingly vindicated.

Not all our wars, however, have been a tonic for the American soul. Iraq, for example, has been a heartbreaker, because our leaders made the foolish presumption that the people there were waiting for the chance to be like us.

And then the Bush administration compounded its error by pretending – until the pretense became completely absurd – that the Iraqi sectarian violence was just like the squabbles of our infant republic in the 18th century. It was a sick joke to claim that the likes of Muqtada al-Sadr had any interest in replicating American constitutionalism.

So now America must regroup. We must get out of Iraq with our honor intact, and we must resolve, once again, to defend our homeland against both murderous terrorists and foolish border-opening politicians – those who would transform America in the name of woozy globalism. This country is all we have. Fortunately, it’s all we need.