In outlining his vision for applying “principled realism” to the war in Afghanistan, President Trump Monday night insisted there will be no precipitous American withdrawal. Though he didn’t specify the number, Trump will be sending additional troops — likely up to 4,000 — to Afghanistan. That would boost our commitment to just above 12,000 men and women in uniform.

And they’ll be expected to accomplish what 140,000 US and allied troops couldn’t achieve at the peak of our engagement, when the Taliban was considerably weaker.

We all must hope that, by a miracle, the new strategy of enhanced training for the Afghan military (and a slap on Pakistan’s wrist) somehow defeats the Taliban. But miracles are in short supply in Kabul. One suspects that this new initiative springs less from rigorous analysis than from the emotional attachment felt by senior officers who’ve seen their troops bleed and can’t bear the prospect of a meaningless sacrifice, of simply walking away.

We have a magnificent, well-led military, but rare is the general who understands the economic principle of “sunk costs,” that you can’t redeem a bad investment by investing even more. When money is gone, it’s gone. The same applies to lives.

A fundamental problem in Afghanistan is that Americans have been dying for a woefully corrupt succession of governments in Kabul for which young Afghans have been unwilling to die. Our new strategy includes a tougher line on corruption, but the damage has been done. What seemed expedient to ignore turned fatal.

Our self-absorbed counter-insurgency strategy assumes that the people will rally around the government we support. But that didn’t happen in South Vietnam, and it didn’t happen in Afghanistan. In both cases, a flood of American wealth turned petty thieves into crime bosses with cabinet posts, while the national army stumbled along and the common man with an empty purse had faint hope of justice.

In Afghanistan, illiterate farmers in remote valleys see their country far more clearly than we do.

As for justice, the Taliban’s religious courts provide it, free of change. It may not be our kind of justice, but it’s better than brazen theft by local officials backed by Kabul. The Taliban are barbaric, woman-hating pederasts, but they’re the home team for Afghanistan’s Pashtun majority, fighting for religious truth, Sharia justice and the Islamist way.

In 2001, we did the right thing by going to Afghanistan to slaughter terrorists. But we were fools to stay. Afghanistan is strategically worthless. Tragically, former President Barack Obama backed the wrong war when his turn came, abandoning the strategic prize of Iraq because of a campaign promise to concentrate on Afghanistan — which he called the right war — to prove his security chops.

Where is the US general with the integrity to ask himself why, after 16 years of American support and self-sacrificing combat, the Afghan central government has been losing province after province to ill-equipped, poorly trained guerrillas who were characterized to me by one of our top generals as tactically inept “idiots”?

I could hear a proud and complacent British general saying the same thing about George Washington’s army. In Afghanistan, we’re the Redcoats.

The Afghans just don’t want what we want them to want. All but crushed, the Taliban came back to conquer. Yes, they received austere aid from Pakistan, but it was nothing compared to the funding and training we lavished on “our” Afghans. The Taliban didn’t have air support, but its fighters believed in their cause.

It really comes down to that blood test: What will men die for? The answer, were we willing to open our eyes, is that more Afghans will volunteer to die for the Taliban than for our dream of a “better” Afghanistan. Nor could the Taliban have survived without support among the population. This is Mao 101.

Well-meaning US officers convince themselves, again and again, that they’ve built a real rapport with their local counterparts, that loyalties are to us, to progress, and that our relationships are about more than the money we’re doling out. We’re renting hookers and expecting love.

Every Afghan who offers a Western handshake is thinking about what he’ll do the minute you’re gone.

We can justify a limited presence in Afghanistan, perhaps 3,000 to 4,000 troops total, for the purpose of killing international terrorists. And we need not stop providing arms to Kabul. But it’s time to stop giving blood.

I hope I’m wrong. I, too, want our casualties to have meaning. But no matter how we reinterpret our mission, there’ll be more American blood. And the only Americans who’ll benefit will be contractors, who love impossible missions that never end.

We cannot save a country that won’t save itself.

Ralph Peters is Fox News’ strategic analyst.