The boys and girls who entered school in September 2001 faced a world altered drastically by the events of 13 years ago today.

In the modern world, and certainly as those cohorts of students got older, it was impossible to shield the young from the tragedies of the World Trade Center or the Pentagon, or the doomed heroism of the brave passengers of Flight 93.

Try as many parents might, the grim images were all too visible.

The attacks came quickly: the first airliner hitting at 8:46 a.m., the second hit at 9 a.m., then the collapse of the twin towers came shortly thereafter. The Pentagon was struck about 9:30 a.m., and the revolt of passengers over Pennsylvania at 10:03 a.m. ended with the hijackers crashing one plane in a field.

The years have brought many remembrances of those days, as well as the ensuing events in Afghanistan and Iraq, where the intractable violence of Islamic fundamentalism continues to threaten American interests and American lives.

The opening of the new museum in New York City is hardly needed to remind us of those days, given the current headlines about airstrikes and beheadings and shootings — Iraq, Syria, Afghanistan, all are a post-9/11 battleground.

In that war on terrorism now fight some of the young people just showing up for school in September 2001. They are now Seaman Jones or Airman Washington, or Private Rodriguez. That long, that the schoolchildren of yesterday are warriors today.

It is an irony that historians will remark upon that a president who opposed the Iraq war as a senator will almost certainly leave office with airstrikes and special-forces operations still underway, ordered in response to the rise of a new set of militants, the Islamic State of Iraq and Syria, or alternatively, the Levant.

The scholars will also continue to debate the relevance of the parallels between ISIS or ISIL, and the al-Qaida conspirators who hijacked airliners for their attacks 13 years ago.

What ties them together is the violence that has knitted into the problems of the Middle East the lives of our young people, thrust into conflicts because of America’s responses to terrorism on our soil.

The debate also will continue whether intervention in Iraq was justified, or whether the Afghanistan war was properly handled, given that Americans are still in harm’s way there 13 years later.

What should not be forgotten is that the United States was attacked from its own skies, by men who abandoned civilization for fundamentalist hatreds that live today. The extirpation of threats to the United States and its allies remains an unfortunate duty for Americans as a people, brought on us 13 years ago.