After more than a week of sporadic far-right violence, a fever seemed to ease in Britain on Wednesday night. An unconfirmed list of more than 30 target sites associated with the migration system, widely circulated online, summoned few would-be rioters but drew a heavy police presence and large crowds of protective counterprotesters.

During the previous days, racist and anti-immigrant rioting had flared in more than a dozen towns and cities across England and in Northern Ireland. Over 400 people were arrested, according to a police chiefs’ group. Many have gone to court. Some are already beginning prison sentences.

The spark for the rioting was anger over a knife attack that killed three young girls and falsehoods that spread online about the perpetrator.

Those participating in the riots have remained a small and strongly unpopular fringe, disowned even by politicians who seek to channel broader public misgivings about immigration. But that has not made the violence easy to stop.

Here is a timeline of how the unrest developed.

Monday, July 29

A stabbing attack that shocked the nation

A knife-wielding attacker burst into a dance and bracelet-making class for young Taylor Swift fans in Southport, a coastal town in northwestern England. His assault killed three girls: Alice Dasilva Aguiar, 9; Elsie Dot Stancombe, 7; and Bebe King, 6. Eight other children and two adults were seriously wounded.