Glancing across this week's dramatic world events, the defeat of the United States Representative for Virginia's Seventh Congressional District in a mid-term Republican Party primary would seem to be of fairly low magnitude – even though that representative, Eric Cantor, was the leader of his party's majority in the House of Representatives.

But Mr. Cantor's defeat means a lot more than you might think for the future of politics in the United States and around the world. It shows, more than ever before, that there is a crisis in conservatism, one that is challenging the basic social compact that allowed the word "conservative" to make electoral sense for nearly half a century.

That word is an awkward vessel uniting those who want government to do less (fiscal conservatives) with those who want government to intrude more on moral grounds (social conservatives). Eric Cantor was very conservative in both senses: An anti-abortion, anti-gay-marriage moralist who tried hard to defeat Barack Obama's modest health-care law and to shut down the U.S. government over an already-stingy budget.

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But he was defeated resoundingly by an even more conservative man, the almost-unknown David Brat, over a single issue: Mr. Cantor's hesitant willingness to pass laws that might give legal citizenship to some of the 12 million Americans of Latin American descent who lack it.

By backing some form of immigration reform, Mr. Cantor was among those Republicans who hoped to make his party one that appeals to ethnic minorities and immigrants – who now represent almost a third of voters in the United States. The 2012 defeat of their presidential candidate Mitt Romney, who won strong majorities of elderly, male and white voters but still lost, divided Republican strategists into two camps.

One camp, led by the party-insider group Resurgent Republic, felt the Romney defeat showed Republicans that theirs ought to become the party of diversity, or it would never win an election again.

They argue that immigrants tend to be natural conservatives: They're more likely than other voters to be small businesspeople (so are fiscal conservatives), and to be religious (so are social conservatives). Canada's Stephen Harper, Britain's David Cameron and Germany's Angela Merkel have all recently tried to make theirs the party of diversity, with varying degrees of success (Mr. Harper has fared the best).

The other camp – the one against which Mr. Cantor crashed and burned – looks at the same figures and concludes that the rising proportion of racial and ethnic minorities is going to make white voters more insecure and fearful, and playing to this fear will drive them to your party. This, for the past 40 years, has been the Republicans' core strategy. The secret to success in American politics, the Republican Party activist Kevin Phillips declared in 1968, is "knowing who hates who" and using that hatred to your advantage.

Mr. Phillips, then an adviser to Richard Nixon, described in a 1970 interview what became known as his "Southern strategy" (known today as the "white strategy"): "The more negroes who register as Democrats in the South, the sooner the Negrophobe whites will quit the Democrats and become Republicans. That's where the votes are." This didn't help Mr. Nixon much, but the approach was central to the election of Ronald Reagan and both Bushs.

Proponents of the "white strategy" (not all members of the hard-right Tea Party) point to a number of recent studies by scholars and pollsters that seem to show that conservative parties stand to gain more white voters from other parties out of fear of diversity than they would gain in minority voters by embracing diversity itself.

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This is a pretty cynical political tactic – one that risks long-term damage to your party's, and your nation's, social fabric. And is based on a view that looks narrowly inside partisan politics, not more broadly at the world.

True, U.S. right-wing Republicans and European far-right parties have been able to chalk up electoral victories recently by appealing to these white voters who are frightened of immigration (they tend to be older and undereducated). As one national survey shows, partisan Republicans and Democrats have polarized themselves more than ever before into mutually resentful "ideological silos." This polarization seems to be happening in many countries.

But that's just the party loyal. The wider population is becoming dramatically more tolerant of racial and religious minorities and of gays – especially in the younger generations. The angry white men may be a tempting slice, but they're no longer the whole pie. The politics of resentment may have driven Mr. Cantor and his ilk out of office, but it will, in the long run, be a losing strategy.