Eight years old. That was the age of one of the youngest known victims of Monday night's massacre in Manchester, England, in which 22 people were killed and 59 injured when a bomb exploded at the end of a concert by American pop singer Ariana Grande.

Yet another apparent "lone-wolf" attack by a disaffected resident of the country where it occurred blows more holes into the notion that a "war on terror" carried out on foreign soil will make any nation safe. The battle must be fought within each homeland's boundaries.

Investigators of the Manchester attack must determine what motivated suspected bomber Salman Abedi, a 22-year-old British citizen whose parents had emigrated from Libya. It is believed that Abedi detonated a homemade bomb in a concourse of the Manchester Arena, killing himself and numerous others. But why?

Islamic State claimed responsibility for the terrorist attack, but its statement via an instant messenger service twice mentioned "explosive devices" while it is believed Abedi set off only one bomb. Even if ISIS was not directly involved, its hateful rhetoric may have inspired Abedi, as it has many of its other would-be followers.

British authorities must engage more with Muslim communities "to understand why people do this," said Richard Barrett, former director of global counterterrorism for M16, that nation's foreign intelligence agency. That's sound advice for every nation susceptible to terrorism, including the United States.

America's terrorist traumas include the murders of 14 people by Major Nidal Malik Hasan at Fort Hood, Texas, in 2009; the deaths of three and injury of 260 others by brothers Tamerlan and Dhozkar Tsarnaev at the 2013 Boston Marathon; and last year's killing of 49 people by Omar Mateen at a gay nightclub in Orlando, Fla.

But what happened in Manchester was particularly appalling. The targets included children, like 8-year-old Saffie Rose Rousos, who came to see a singer they used to watch on Nickelodeon. "I don't have words," Grande tweeted after the bombing. It's hard to know what to say except, our children must be kept safe.