(sfôr'tsä), Italian family that ruled the duchy of Milan from 1450 to 1535. Rising from peasant origins, the Sforzas became condottieri and used this military position to become rulers in Milan. The family governed by force, ruse, and power politics. Under their rule the city-state flourished and expanded. Similar to the Medici in their use of personal power, the Sforzas differed in that they were warriors, not bankers.
The first prominent member of the family was Muzio Attendolo Sforza, 1369–1424, a farmer from the Romagna who became a noted condottiere and took the surname Sforza [the forcer]. He fought in the service of several Italian states, then became involved in the struggles for the succession to the kingdom of Naples and died while serving Queen Joanna II in her efforts to retain the throne. His illegitimate son, Francesco I Sforza (see Sforza, Francesco I), became duke of Milan in 1450 through his marriage to Bianca Maria Visconti, daughter of the last Visconti duke of Milan.
Francesco was succeeded by his eldest son, Galeazzo Maria Sforza, 1444–76, a highly educated but dissolute and cruel man; he was a patron of the arts and employed the architect Bramante. He was assassinated in the Church of San Stefano at Milan by republican conspirators, but the popular uprising anticipated by the assassins did not materialize. Another of Francesco's sons, Ascanio Maria Sforza, 1455–1505, was a cardinal of the Roman Catholic Church and also a patron of the arts. He secured the election of Rodrigo Borgia (Pope Alexander VI) as pope.
Galeazzo's daughter Bianca Maria married Holy Roman Emperor Maximilian I, and his illegitimate daughter Caterina Sforza, 1463?–1509, became the wife of Gerolamo Riario, lord of the cities of Imola and Forlì and a nephew of Pope Sixtus IV. After Gerolamo was murdered (1488), Caterina ruled both cities until she lost them to Cesare Borgia in 1499. With her second husband, Giovanni de' Medici, she bore a son who became the famous condottiere Giovanni delle Bande Nere (see Medici, Giovanni de').
Galeazzo's wife, Bona of Savoy, acted as regent for their son, Gian Galeazzo Sforza, 1469–94, who succeeded to the duchy as a minor on his father's assassination. However, in 1480, Galeazzo's brother Ludovico Sforza (see Sforza, Ludovico) deprived his nephew of the duchy and assumed its control. Gian Galeazzo died a virtual prisoner. His daughter, Bona Sforza, married Sigismund I of Poland. In the Italian Wars Milan was claimed by Louis XII of France, great-grandson of Gian Galeazzo Visconti. Ludovico lost Milan to Louis in 1499, but in 1512 the Swiss, as members of the Holy League against France, stormed Milan and installed Ludovico's son, Massimiliano Sforza, 1493–1530, as its duke. The Swiss actually controlled Milan until their defeat at Marignano (1515), which obliged Massimiliano to surrender Milan to Francis I of France; Massimiliano retired to France.
Holy Roman Emperor Maximilian conferred the title of duke of Milan on Massimiliano's brother, Francesco II Sforza, 1495–1535. Francesco took possession of his duchy after the French defeat (1522) by the army of Holy Roman Emperor Charles V at Bicocca. Accused by the imperial general Pescara of plotting against Charles, Francesco was deprived (1525) of most of his duchy. He joined (1526) the League of Cognac against the emperor, but was obliged to surrender to the imperial troops that besieged him in Milan. After the Treaty of Cambrai (1529), Francesco was restored as duke and ruled until his death. He had no heirs, and the succession to Milan once more was contested by France and Spain, with Spain emerging victorious in the Treaty of Cateau-Cambrésis (1559).