Tensions between the comfortable middle-class suburbs and the rest of the country grew steadily in the closing decades of the 20th century, as the gap between the educated and well paid and the uneducated and ill paid steadily widened. Class division came into existence between those who made ''professional'' salaries and those whose hourly wage kept sinking toward the minimum. But the politicians pretended to be unaware of this steady breakdown of fraternity.

Our nation's leaders, in the last decade of the old century and the first of the new, seemed never to have thought that it might be dangerous to make automatic weapons freely and cheaply available to desperate men and women -- people without hope -- living next to the centers of transportation and communication. Those weapons burst into the streets in 2014, in the revolution that, leaving the cities in ruins and dislocating American economic life, plunged the country into the Second Great Depression.

The insurgency in the ghettos, coming at a time when all but the wealthiest Americans felt desperately insecure, led to the collapse of trust in government. The collapse of the economy produced a war of all against all, as gasoline and food became harder and harder to buy, and as even the suburbanites began to brandish guns at their neighbors. As the generals never stopped saying throughout the Dark Years, only the military saved the country from utter chaos.

H ere, in the late 21st century, as talk of fraternity and unselfishness has replaced talk of rights, American political discourse has come to be dominated by quotations from Scripture and literature, rather than from political theorists or social scientists. Fraternity, like friendship, was not a concept that either philosophers or lawyers knew how to handle. They could formulate principles of justice, equality and liberty, and invoke these principles when weighing hard moral or legal issues. But how to formulate a ''principle of fraternity''? Fraternity is an inclination of the heart, one that produces a sense of shame at having much when others have little. It is not the sort of thing that anybody can have a theory about or that people can be argued into having.

Perhaps the most vivid description of the American concept of fraternity is found in a passage from John Steinbeck's 1939 novel, ''The Grapes of Wrath.'' Steinbeck describes a desperately impoverished family, dispossessed tenant farmers from Oklahoma, camped out at the edge of Highway 66, sharing their food with an even more desperate migrant family. Steinbeck writes: '' 'I have a little food' plus 'I have none.' If from this problem the sum is 'We have a little food,' the movement has direction.'' As long as people in trouble can sacrifice to help people who are in still worse trouble, Steinbeck insisted, there is fraternity, and therefore social hope.

The movement Steinbeck had in mind was the revolutionary socialism that he, like many other leftists of the 1930's, thought would be required to bring the First Great Depression to an end. ''The quality of owning,'' he wrote, ''freezes you forever into the 'I,' and cuts you off forever from the 'we.''' Late-20th-century liberals no longer believed in getting rid of private ownership, but they agreed that the promise of American life could be redeemed only as long as Americans were willing to sacrifice for the sake of fellow Americans -- only as long as they could see the government not as stealing their tax money but as needing it to prevent unnecessary suffering.

The Democratic Vistas Party, the coalition of trade unions and churches that toppled the military dictatorship in 2044, has retained control of Congress by successfully convincing the voters that its opponents constitute ''the parties of selfishness.'' The traditional use of ''brother'' and ''sister'' in union locals and religious congregations is the principal reason why ''fraternity'' (or, among purists, ''siblinghood'') is now the name of our most cherished ideal.