Some may find it surprising that the perpetrator of the recent horrific New Zealand terrorist attack that killed fifty Muslim worshipers in two mosques, combined seemingly right-wing nationalism with seemingly left-wing socialism and environmentalism. He hates nonwhite immigrants to Western nations, but also hates capitalism and capitalists, and believes that we must take draconian measures to stave off environmental catastrophe. People who perpetrate "lone wolf" terrorist attacks often have strange and idiosyncratic ideas. But in this case, the terrorist's worldview is less unusual than it might seem. A similar combination of views is evident in many xenophobic nationalist movements, both past and present. Socialists and nationalists have their differences. But they also have much in common, including a zero-sum view of the world.

Anti-immigrant nationalist parties in Europe often combine hostility to nonwhite immigration with support for extensive government control of the economy. That's true of such cases as the National Front in France (now renamed as the "National Rally") and the AfD in Germany. Such parties often also often blame immigrants for real and imagined environmental degradation, just as the perpetrator of the New Zealand attack does. Numbers USA, one of the most influential anti-immigration organizations in the US, has similar views, including advocating coercive population blaming immigrants for environmental degradation. James Tanton, a founder of the organization and other leading restrictionist groups is also a longtime advocate of coercive population restriction.

Similarly, the perpetrator of the New Zealand attack argues that environmentalism and immigration restriction "are the same issue [because] the environment is being destroyed by over population, we Europeans are one of the groups that are not over populating the world. The invaders are the ones over populating the world. Kill the invaders, kill the overpopulation and by doing so save the environment." Some influential far-left environmentalists have also advocated coercive population control, including defending China's cruel "one child" policy.

In the early twentieth century, the Nazis promoted an even more extreme form of racial nationalism, and combined that with even more extreme government control over the economy. Hitler advocated extermination of the Jews and the conquest of other European nations primarily because he had concluded that that was the only way Germans could survive and prosper in a zero-sum world.

Racial nationalists and socialist far leftists share a common zero-sum view of the world under which some groups can succeed and prosper only at the expense of others. It is easy to see how that sort of world view often leads adherents to believe that drastic action—including violence—is essential to ensure that the "right" people end up as winners in this cruel zero-sum world. I discussed this crucial commonality in greater detail here:

Psychologists find that people are often naturally suspicious of "out groups" different from their own, and therefore more likely to suspect them of nefarious activities of various kinds… Many Americans worry about our trade deficit with Japan or Mexico in a way that few do about New York's trade deficit with Iowa, or their personal trade deficits with their local supermarket. This, despite the fact that economists across the political spectrum recognize that none of these deficits actually say anything meaningful about our economic performance. In addition to helping stoke fear of out groups, ignorance also exacerbates prejudice by contributing to the perception that the world is a zero-sum game. As Donald Trump likes to put it, nations like Mexico and Japan are "winning" and the United States is "losing" because they sell more goods to us than we do to them. Similarly, if Group A is doing well, it must be at the expense of B, C, and D. Understanding the fallacy of such thinking requires some knowledge of basic economics, and often also some reasonably careful reflection about the evidence… The Nazis held a particularly extreme version of the view that the world economy is a zero-sum game. But more moderate – yet still dangerous – versions of the same world-view remain common on both right and left. Zero-sum thinking need not always lead to racial and ethnic hostility, or xenophobia. It is also often channeled in other directions, such as hostility to the wealthier members of one's own ethnic group or society. In some cases, it leads to a combination of both fear of foreigners and fear of the wealthy. For example, unexpectedly popular Democratic presidential candidate Bernie Sanders echoes Donald Trump's hostility to international trade, while simultaneously arguing that ordinary Americans can only be economically successful by redistributing vast wealth from "the 1 percent." Until recently, he also expressed considerable hostility towards immigration, denouncing the idea of free migration of labor as a plot by "the Koch brothers" and other malevolent billionaires, which would impoverish the working class and end up "doing away with the concept of a nation state." Still, zero-sum thinking often leads to fear of out groups, such as foreigners or minorities. If the world is a zero-sum game, we often naturally assume that our only recourse is to ensure that "our" group ends up among the "winners" rather than the "losers," as Trump might put it. Although often associated with the nationalist right, such thinking is not limited to any one side of the political spectrum. In both America and Europe, left-wing political movements have often been susceptible to it, as well – a pattern evident in the hostility of many early-twentieth century Progressives to immigrants and racial minorities, and in the recent rise of left-wing anti-Semitism in Europe.

Fortunately, most nationalists and socialists aren't willing to go so far as to personally commit acts of terrorism. But all too many are willing to advocate large-scale coercion that inflicts great harm on large numbers of people, in order to ensure that they and their preferred causes don't end up as losers in a zero-sum world. Everything from barring migrants fleeing horrible oppression, to separating immigrant children from parents in order to deter them from entering, to coercive population control, to massive expropriation of property, and repression of "capitalists" in order to transfer the nation's wealth to "the people." The list can easily be extended.

There is no easy way to combat zero-sum thinking on either the left or the right. Both have deep roots in a combination of political and economic ignorance and basic human psychology, which makes us susceptible to "in group-out group" hostility. But perhaps the beginning of wisdom is to recognize that most of our economic and social interactions do not have to be zero-sum games in which gains for one group must come at the expense of another.

Far from enriching natives, immigration restrictions often end up undermining their freedom and prosperity as well as that of potential immigrants. Standard economic estimates indicate that free migration throughout the world would double world GDP, with many of the gains going to natives, not just migrants. Natives lose the gains from trade with immigrants, and also suffer from the civil liberties violations inherent in efforts to keep out and deport migrants. Rich and poor are not locked in a zero-sum game either. To the contrary, they can prosper together through mutual exchange, and historically often have.

Pollution and global warming are genuinely serious problems. But addressing them does not require massive coercion or keeping millions of people in poverty. Historically, increasing wealth has actually led to reductions in pollution (after an initial increase early in the process of industrialization), as wealthy societies can more easily afford to invest in reducing pollution. Even when it comes to the particularly difficult challenge of climate change, there are ways to combat that simultaneously increase prosperity rather than stifle it. They include reducing regulatory obstacles to using nuclear power, cutting back on zoning restrictions that make it hard to build denser housing, and offering prizes for the development of new "clean" energy technologies. Where regulation is needed to cut back on carbon dioxide emissions, it should take the the scalpel form of a revenue-neutral carbon tax, rather than the meat cleaver of coercive population control and government takeovers of huge portions of the economy.

It would be naive to imagine that zero-sum games never occur. But they are far less common than either the far left or the nationalist right imagine. The more people come to understand that, the better.

NOTE: Because perpetrators of terrorist attacks often undertake them in large part to gain fame and media attention for themselves and their ideas, I have refrained from mentioning the name of the man who committed the New Zealand attack or linking to his "manifesto." I have instead linked to this helpful summary of his ideas, by James Peron. However, both the name and the manifesto are easily found online, for those who wish to read it for themselves.

UPDATE: In the original version of this post, I stated that Numbers USA advocates "coercive population control." However, while that is true of John Tanton, who helped found the organization, I have not seen evidence that the organization promotes that idea today. Accordingly, I have edited the relevant part of the post to reflect that fact. I apologize for the mistaken conflation in the initial version.