ROCHESTER, Minn. — It's now been 18 years since Sept. 11, 2001 — the 9/11 terrorist attacks on the United States.

Is that enough time to gain a historical perspective on what it all means?

"It's generally a minimum of 10 years, but usually about 20 years is better," said Chad Israelson, a history instructor at Rochester Community & Technical College.

"In 20 to 30 years, we can say, 'Oh, that caused this now,'" he said.

By that calculation, we're getting close to having some idea of the long-term effects of 9/11 on American society and politics. Consider, for example, the war on Iran, the surveillance state, military spending, airport security, anti-Muslim sentiment, even, as Israelson pointed out, failed peace negotiations last week at Camp David. "There are still reverberations continuing," he said.

Things change

As a history teacher, Israelson is aware that how we see an event — in this case the 9/11 attacks — at present, might not be how we view it in the future.

That's not news to history teachers and historians.

"Revisiting and often revising earlier interpretations is actually at the very core of what historians do," states the National Council on Public History. "And that’s because the present is continually changing."

As the council notes, "It’s not simply that new facts come to light, but that the shape and meaning of historical events look quite different from different vantage points and time periods."

In other words, the 20 or 30 years down the road mentioned by Israelson are likely to bring new facts to light, or to give a different point of view on what happened and what it means. Our perspective changes over time.

For Israelson's students at RCTC, 9/11 can seem long ago and far away.

"These kids were maybe born, maybe a year old, when it happened," he said. "To them, it's like the Vietnam War was for me."

Those who lived through 9/11, on the other hand, might view it much like an earlier generation viewed Pearl Harbor.

"When you teach it, the appreciation for how big it was at the time, you almost had to be around at the time to understand it," Israelson said.

Will it still appear that big decades from now? Time will tell.