Ten years ago this morning, our world changed forever. On Sept. 11, 2001 — a date that would forever after be referred to simply as 9/11 — radical Islamic terrorists hijacked three jetliners and used them as missiles in a war against Americans and the American way of life.

The death and destruction they wrought was nightmarish. More than 3,000 people died in New York, Washington and Pennsylvania, surpassing the loss of life suffered from the Japanese attack on Pearl Harbor.

A decade later, even after American forces killed terrorist mastermind Osama bin Laden, we still struggle to grasp the horror of 9/11, the burden of the war it spawned and their effects on the American psyche.

Perhaps the most terrifying factor about 9/11 was that the attacks occurred on the American homeland, which for 200 years had been largely protected from foreign enemies by the distances that separated us. Even during the volatile years leading up to 9/11, when terrorism spread around the world like a deadly virus, America suffered harder blows from homegrown murderers such as Oklahoma City bomber Timothy McVeigh than from foreign-born jihadists.

The morning of 9/11 changed that — immediately, decisively and permanently. The attacks were shocking and indisputable evidence that our world had become not only much smaller but also much meaner, and that the American homeland was no longer insulated from the meanness.

Thomas E. Franklin / Bergen County Record

Firefighters raise the U.S. flag at the World Trade Center site in New York City on Sept. 11, 2001, as work continued after hijackers crashed two airliners into the center’s twin towers. A total of 2,753 people died at ground zero.

In that instant we began a painful transformation from a society that until then had remained remarkably free — and largely carefree — into a nation consumed by the desperate need to protect its people.

That concern — and the determination to fight the enemy halfway around the world rather than here at home — led to the war on terror, which is still very much under way on this anniversary.

After a decade of fighting, the scope and the cost of the war are sobering to comprehend.

So far, America has lost more than 6,000 military personnel in the course of the war. To put that in perspective, consider that 4,435 of our forefathers lost their lives in the American Revolution.

Consider also the duration of the war on terror — 10 years so far. Combat in the American Revolution spanned eight years, while the Civil War and World War II each lasted for four years. And America’s involvement in World War I — “the war to end all wars” — was two years.

So if it seems this conflict has lasted a very long time, it has. And because of the nature of the enemy — an idealistic, religion-driven foe that has no government to sue for peace and no inclination to do so anyway — it is a war that will go on indefinitely.

The doughboys of World War I sang “Over There,” a ditty pledging that “we won’t come back till it’s over, over there.” It would be impossible to make that pledge today.

“Over there” in the war on terror can be anywhere from Kandahar to Kansas City. And it won’t be over as long as there are those who hate Americans and the American way of life — extremists who were encouraged and emboldened by the devastation of 9/11.

That unrelenting sense of a permanent struggle underlies the biggest changes to America as a result of 9/11.

Because of the nature of our enemy and the ongoing necessity to protect ourselves, American life in the post-9/11 era is undeniably less free than it was on Sept. 10, 2001. Not only do we have body scans and pat-downs in our airports and many public buildings, but we have given government unprecedented authority — sometimes explicitly, sometimes implicitly — to use measures ranging from wiretapping to waterboarding to pre-emptive military strikes to keep us safe.

There is an inherent conflict between such actions and Americans’ historic approach to living as a free people. Before 9/11, Americans and their government generally operated under the presumption that our hard-won liberty justified a certain level of risk. Americans also felt intuitively that the good guy always wins in the end, even if the bad guy shoots first. And since we were the good guys, we had the luxury of taking the high road.

The devastation of 9/11 shook those perceptions to the core and changed the way we looked at national security and at the conduct of war.

We changed not only the way we dealt with terrorists themselves, but even with the potential for terrorism. Complex anti-terrorism plans were drawn up by virtually every governmental entity from the U.S. Department of Transportation to rural water cooperatives with smiley faces painted on their storage tanks.

There is little doubt that we are safer now than we were then, thanks to the sacrifice of our military and a marked improvement in the effectiveness of our intelligence community.

The fact that we have so far avoided further attacks on the scale of 9/11 would seem to suggest that the end justifies our means. But that does not necessarily mean we feel good about it.

The old saw that “freedom is not free” has been proven true once again, but so has a sad new truth: Freedom is not quite what it used to be.

We are reminded of both truths every time we hear of another deployment from Fort Hood, every time we hear a debate about enhanced interrogation techniques, every time we hear of another terrorist leader who has been killed. And every time we go through metal detectors at the local courthouse.

We are, thank God, still a free people. And even as we endured the national transformation made necessary by 9/11, the months and years since have shown we are still a compassionate people, as well as a people capable of unity, commitment and sacrifice.

But while that essential goodness remains in Americans, there can be no doubt that we are a changed people and that change has been excruciatingly painful. We are a country that is still very much in mourning — not only for those we lost, but for the innocence that we lost as well.

To America, 9/11 is the tear that wouldn’t dry.