A generation of young Americans have been reminded brutally of the price we pay for letting down our guard against murderous enemies.

Nineteen years ago today, on Sept. 11, 2001, the foes were terrorists based abroad, who massacred 2,997 people in New York City, Washington, D.C., and on an airplane that crashed in rural Pennsylvania.

U.S. intelligence agencies knew the terrorists were planning to attack our homeland, but our defenses were pitifully — inexcusably — weak. We continue to honor the heroes of that day as we vow never again to allow our security against such an assault to be weakened.

Now we are under attack again, by an enemy of all humankind. It is COVID-19, a virus that by this week had killed 190,000 Americans. It is likely the global death toll will top a million.

While most local residents were insulated by distance from danger at the 9/11 massacre sites, we have not been as lucky with this second assailant. This time, the enemy is among us. Locally, we have seen thousands of cases. In Trumbull County, the virus has claimed the lives of 126. In Mahoning County, 272 have perished.

During the years prior to 9/11, we ignored the warnings about violent extremists who meant to come here and kill as many Americans as they could. Likewise, we had to learn that foreign organizations were capable of recruiting our fellow Americans to murder us in assaults that, while smaller in magnitude than 9/11, continue.

We took dramatic action to prevent such violent sprees. Now, we have at least some protection against them.

But not against viral foes. Infectious disease researchers have warned for years that microbes have the power to kill worldwide. Our reaction to that was to go about our merry ways, to the extent that even stockpiles of medical equipment and supplies needed to combat an epidemic were depleted and not restocked.

Prior to 9/11, we ignored warnings and paid a terrible price. The same thing happened with COVID-19 — and, even as the pandemic continues, there is evidence many among us have not joined the fight to save lives.

After 9/11, we recognized other terrorists, both foreign and domestic, had to be guarded against.

Do we understand that about enemies we cannot see? There will be a next time. Are we prepared to do what is necessary to guard against that?