The Australian-born gunman who killed 50 people at a mosque in Christchurch, New Zealand, last week cited US President Donald Trump as “a symbol of renewed white identity and common purpose” with his murderous white-supremacist cause. Trump condemned the massacre and said he was being unfairly blamed for it, setting off a familiar argument over the impact of his fondness for stoking existential fears among many white people around the world. He has indeed spoken, like the mass shooter, of immigrants as “invaders” and Islam as a “problem.”   But a rush to blame Trump for inciting racial hatreds obscures the enduring power of historical Australian white supremacism. For the settler colony, whose unparalleled "whites only" policy restricted non-European immigration from 1901 until the late 1960s, has defined a global culture of besieged whiteness. Trump himself acknowledged as much in January, 2017, eight days into his presidency, when he confessed his admiration for Australia’s brutal measure of detaining refugees on remote islands. “That is a good idea; we should do that too,” he told Malcolm Turnbull, then Australia’s prime minister, adding, “You are worse than I am.” Living next door to Asia, many white Australians felt most keenly the racial fear of being overwhelmed or overtaken by dark-skinned peoples, especially as globalization and mass immigration accelerated in the late 19th century. The Christchurch killer’s argument for racial self-defense eerily echoes an 1893 text of white supremacists around the world titled “National Life and Character: A Forecast.” Authored by a British-educated Australian academic named Charles Henry Pearson, it claimed that white men were in danger of being “elbowed and hustled, and perhaps even thrust aside” by “black and yellow races.” Identifying China as a threat to white domination, Pearson urged his readers to defend “the last part of the world, in which the higher races can live and increase freely, for the higher civilization.” His ideas were heeded by Australian politicians, who instituted a “White Australia” policy shortly thereafter, and by Australian media barons such as Keith Murdoch (father of Rupert), who enlisted their newspapers in the cause of racial unity. They also had a “great effect,” US President Theodore Roosevelt wrote to Pearson, among “all our men here in Washington.” Pearson was also read attentively in Canada, New Zealand and South Africa. In “The Rising Tide of Color Against White World-Supremacy,” a bestselling 1920 racist tract inspired by Pearson, Lothrop Stoddard, an American lawyer, historian and philosopher of nativism, admired “the instinctive and instantaneous solidarity which binds together Australians and Afrikaners, Californians and Canadians, into a ‘sacred Union’ at the mere whisper of Asiatic immigration.” Exposed to the “increasing virulence” of white supremacism, the African-American thinker W.E.B. Du Bois fearfully predicted in 1910 that the “problem of the 20th century is the problem of the color line – the relation of the darker to the lighter races of men.” That problem has resurfaced in our own time, with terrorism, China and mass immigration rising against a background of economic uncertainty. But the terror of racial extinction and longing for extreme measures against dark-skinned people long preceded Trump, and they were openly expressed by respectable members of the sacred union. In 2007, the novelist Martin Amis told a wholly unfazed journalist from the Rupert Murdoch-owned Times of London: There’s a definite urge — don’t you have it? — to say, “The Muslim community will have to suffer until it gets its house in order.” What sort of suffering? Not letting them travel. Deportation — further down the road. Curtailing of freedoms. Strip-searching people who look like they’re from the Middle East or from Pakistan. Challenged later, Amis said he wasn’t advocating these measures but was merely “describing an urge.” The Canadian columnist Mark Steyn hoped in 2006 in “America Alone: The End of the World as We Know It,” that Europeans will eventually figure out what the Serbs already had in their war against Bosnian Muslims: “If you cant outbreed the enemy, cull em.” Steyn “rejoiced” in Trump’s victory in 2016, explaining later that “the more diverse you get, the more stupid you get,” and that “we do not want to be in a world where Western civilization slides off the cliff.” It’s no accident that Trump’s most powerful supporter (and enabler) is a media baron born and raised in white Australia. And the Australian senator who insisted last year on a “final solution” for immigration involving bans on Muslims and others “from the third world” was at least partly emboldened by a global culture of white supremacism fostered by the Murdoch media. Blaming Trump for racist outrages is easy. But attempts to erase the color line should start by recognizing the way it was drawn in the late 19th century in Australia, and how it re-emerged with appalling consequences for today’s racially mixed societies. Bloomberg View