The journey of hundreds of commuters into the center of London was brutally interrupted by a dull explosion and a flash of flame as a train stood at Parsons Green station on Sept 15. That evening, the trains were running as normally as before, and people went to the theater, restaurants and bars as if nothing had happened.

No one was seriously injured in perhaps the 215th terrorist attack on London since 1867, when Irish radicals detonated a bomb that killed 12 people. And few seemed to pay much attention.

London has long been the target of terrorists and also an arena where disputing parties have settled scores. The London Underground was first bombed in 1883. Of those 215 attacks - the figure is a rough count - 162 were carried out by Irish republicans and the rest by anarchists, Palestinian groups, right-wing extremists and Scottish nationalists. Only eight have been carried out by Islamists, all since 2005. Recent attacks are closely linked to a series of deadly attacks in Barcelona, Brussels, Berlin, Nice and Paris.