The two men mix rage with self-pity. They see themselves as victims and use terms like “invasion,” “mass immigration” and “white genocide” to describe what they regard as the destruction of Europe and the white race. Both the Australian and the Norwegian barely mention their own homelands and focus on Europe and the United States. Mr. Tarrant sees the white population of Australia and New Zealand as Europeans.

He writes how he decided on his “final push” after visiting France in 2017, where he saw how the European French had been “replaced” by “nonwhites.” Thus the title of his manifesto: “The Great Replacement.”

Like the Norwegian, Mr. Tarrant is obsessed with birthrates and describes Europe as growing weaker and older. The Norwegian terrorist wanted to establish state-run birth clinics where blond, blue-eyed mothers would give birth to a dozen children each. Mr. Tarrant wants to restore what he calls “traditional family values.”

Even though Mr. Tarrant’s manifesto is tailored to his dark web audience, sometimes with coded language, he tries to create a background of normalcy by quoting poems by Rudyard Kipling and referring to more mainstream right-wing figures. Likewise, Mr. Breivik frequently quoted people like Thomas Jefferson, as if he were the rightful heir to well-established ideas.

Their main agenda is the same: to crush Muslim immigration. Mr. Tarrant wants to “deport those invaders already living on our soil.” Mr. Breivik suggested that every Muslim should be given the opportunity to convert to Christianity and take a Christian name. Those who do not obey should be deported or executed. All examples of Islamic art should be destroyed including all mosques; languages like Arabic, Persian, Urdu and Somali would be banned.

One of the mosques targeted in New Zealand is built on the site where a church once stood. While the Christchurch gunman aimed straight at his targets, Mr. Breivik wanted to kill the so-called traitors, the members of the liberal elite and ruling Labour Party who had let Muslims into the country.

Both men wrote about sacrificing themselves to a greater cause and envisioned that they would be released from prison by their followers after a “conservative revolution”swept through the world.