A Utah man was among the three victims in the...

A Utah man was among the three victims in the attack outside the UK parliament in London on March 22, 2017. Credit: Getty Images / Carl Court

London will keep calm and carry on, just as it has for 2,000 years of extraordinary history and occasional upheaval, just as all free and vibrant cities must.

The words of Prime Minister Theresa May after an attack on Westminster Bridge were the perfect answer to the violence of zealots: “Yesterday, an act of terrorism tried to silence our democracy,” May said. “We are not afraid, and our resolve will never waver in the face of terrorism.”

British-born and Islamic State-inspired terrorist Khalid Masood used a car and knife to kill three people on Wednesday. One was American Kurt Cochran, there celebrating his 25th wedding anniversary with his wife, who was one of more than 30 wounded. Others injured were from at least eight nations. Several were schoolchildren. The attacker was shot to death by police.

The setting is a tourist magnet, yards from Big Ben and Parliament. The announcement that Masood has a criminal history and had been investigated by British intelligence only reinforces the difficulty of stopping such plotters. The Islamic State is calling Masood a “soldier” in its fight against nations like Britain and the United States involved in military operations in the Middle East, nations trying to stop the vicious attacks ISIS itself levels against civilians in the region. No doubt the attacks will again raise often misplaced warnings about the horrors of immigration, but Masood’s story actually highlights the opposite pattern, and the difficulty of stopping such violence: most domestic terrorists committing atrocities in Western nations are homegrown.

The world is dangerous. In an incident Thursday in Antwerp, Belgium, a driver used a car in an unsuccessful attempt to attack pedestrians. These acts must be answered with a mindful pursuit of security tempered by a redoubled dedication to freedom. — The editorial board