Born the same day as the turn of the twentieth century, Alfredo Berlinghieri (De Niro) and Olmo Dalcò (Depardieu) come from opposite ends of the social spectrum. Alfredo is the son of a rich landowner, while Olmo is an illegitimate peasant son. As Alfredo is somewhat rebellious and despises the falseness of his family, in particular his father, he befriends Olmo, who is brought up as a socialist.

The two are friends throughout their childhood, despite the social differences of their families. Olmo enlists with the Italian army during World War I and goes off to fight while Alfredo learns from his father how to run his family's large plantation. Olmo returns from the war and his friendship with Alfredo continues. However, Alfredo's father has hired Attila Mellanchini (Donald Sutherland) as his foreman, a sadistic man who becomes taken with fascism, eventually incorporating his new belief system in his dealings with the Berlinghieri workers; he treats them very cruelly and later cages them in the Berlinghieri compound and them of being traitors to fascist Italy. Several are killed by Attila himself. As the new padrone of the plantation, Alfredo does little to challenge or halt Attila's actions.

The intimacy and lack thereof in their respective relationships with others is highlighted in their love lives. Alfredo marries a gorgeous, demure woman while Olmo marries Anita, who like him shares in the enthusiasm of the cause of workers' rights. Alfredo’s wife, Ada, sinks into alcoholism when confronted with the reality of the emptiness of her relationship with Alfredo. Anita, a strong and independent spirit dies tragically an almost martyr’s death; she dies in childbirth, bringing another member into the community. As Olmo takes on his fateful role of leader among the poor farmers and their families, he clashes with Attila.

The power however shifts after World War II, and the ruling class is at the mercy of the jovial and bitter peasants in the town. As padrone, Alfredo is captured by a teenage peasant boy carrying a rifle. Attila is also captured when he and his wife, the equally cruel and sadistic Regina (Laura Betti), try to flee the region. Attila is stabbed, non-fatally, several times by women wielding pitchforks and is imprisoned in the Berlinghieri pig sty. He his later executed by the peasants (while they cut off most of Regina's hair), who have discovered that Attila killed a young boy several years prior in a fit of rage and drove a wealthy landowner, Pioppi, to suicide in order to steal his land and home. Regina and Attila had also murdered Pioppi's wife (Alida Valli), whom had become obsessed with avenging her husband's death.

Alfredo is brought before Olmo's socialist contingent to stand trial. Many workers come forth and accuse Alfredo of letting them suffer in squalor while he (and his social class) profited from their labors. Though Olmo calls for his execution, Alfredo is allowed to live when the Italian partisans arrive and announce the new post-war laws that require all peasants to hand over their firearms until a stable government can be established.