If a country proves unable to govern itself, you expect to find a historical explanation. A plague, maybe, or chronic drought, or the rise of a hostile power on its borders.

None of those applies in the present case. To the contrary, by many measures the United States, long blessed, should be entering a new golden age. Who would have predicted 10 years ago that the United States would become, as the Wall Street Journal reported last week, the world’s No. 1 energy power — producing more oil and gas combined than Russia or Saudi Arabia? While most developed nations, from Japan to Italy to Russia, don’t have enough young people, U.S. population trends are relatively benign thanks to immigration and a stable birth rate.

Yet the government seems unable to do its job. The shutdown can be blamed on the reckless, irresponsible miscalculations of congressional Republicans. But the shutdown is only the most extreme example of government’s failure to solve solvable problems: to fix Social Security, pass a budget, reform immigration laws. What gives?

One theory is bad luck: Some analysts suggest that John Boehner, Harry Reid and Barack Obama are a collection of unusually weak leaders, or leaders especially ill-matched in temperament.

A variation on that theme holds that leaders of the previous generation were the aberration: Men (mostly) whose world views were formed in World War II and the Cold Warunderstood the nature of existential threats and were willing to put aside partisan interest for the nation’s good. Today’s partisanship is just a return to normal.

But maybe even larger trends are at work. Here are a few possible culprits:

Slow growth and inequality. As my colleague Robert Samuelson recently wrote, after World War II Americans became accustomed to 3 percent annual growth, which allowed for a cheerful spreading of the wealth. Now 2 percent may be the new normal, in part because the United States, though its population is younger than that of many countries, still will have more retirees per active worker than in the past.

The growth we do manage is being shared less equally, thanks largely to technology and globalization. The possible result: nastier politics as classes and generations fight over a slower-growing pie.

The great fracturing. Then-Sen. Barack Obama electrified the nation in 2004 with his Democratic convention speech insisting there was no Red America or Blue America. Since then, the divisions have only become more marked. From guns to gay marriage to Obamacare, we seem to live in two separate countries whose inhabitants lack the empathy or even the language to understand each other.

As Americans increasingly choose to live among those with whom they agree politically, in what author Bill Bishop called “the big sort,” technology and other factors loosen the ties that bound us into one nation. Other than the occasional, and fleeting, YouTube video, there is no cable television channel or Internet site that we experience in common. Political parties that transcended region have been purged of dissenters and overshadowed by single-focus interest groups.

Immigration and the end of a white majority.The Mexican migration, and the similarly large migration of others from the rest of Latin America, has in just one generation reshaped the nation,” Michael Barone recently wrote. In 1970 there were fewer than 1 million Mexican-born people in the country; today they number more than 12 million, and with their children comprise about 10 percent of the population.

Meanwhile, for the first time, racial and ethnic minorities — if that’s still the right word — make up about half of the under-5 population. By 2043, whites will no longer be in the majority. The country seems to have handled the surge in immigration more peaceably than it greeted past waves of newcomers. But the shifts may be causing political shockwaves whose connections to the demographic changes aren’t immediately obvious.

Inadequate political institutions.There’s the affront posed to the principle of one man, one vote by the U.S. Senate, where 600,000 Wyoming residents have as much say as 38 million Californians. In an increasingly self-serving redistricting process, politicians choose their voters instead of the other way around and insulate themselves from challenges by all but the extremes. The frantic money chase drives good people out of politics.

The contrast between the country’s relative advantages and its Washington dysfunction is frustrating, but maybe that, too, is part of the problem: In an apparently benign environment, when foreign enemies again seem distant and unthreatening, nothing scares the politicians toward compromise. They manufacture one ginned-up crisis after another, but the deadlines fail to provide the hoped-for jolt toward progress — even when, as now, millions of blameless Americans suffer for politicians’ failings.

Will it take a crisis not of their creating to change the dynamic? Let’s hope not.

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