LONDON — Last Friday was the first anniversary of the assassination of Jo Cox, the British member of Parliament who was killed by Thomas Mair, now serving life in prison for her murder. “This is for Britain,” he shouted as he stabbed and shot to death Ms. Cox, a 41-year-old Labour Party politician and mother of two, a week before the Brexit referendum. As shocking as this attack was, it did not come without precedent. In recent years, there have been noticeable upticks in far-right violence, even if its frequency and deadliness have often been overshadowed by the more high-profile attacks claimed by the Islamic State.

The frequency of far-right attacks is particularly significant in the United States, where white supremacist, anti-government and neo-Nazi extremists have been responsible for 73 percent of deadly terrorist attacks since Sept. 11, 2001, according to the Government Accountability Office. Also notable is that in many cases, Muslims have become the target of violence.