What dance style from Cuba is the foundation of modern salsa?

Cuban son is the Cuban dance-and-music style that forms the foundation of modern salsa.

Son cubano developed in eastern Cuba during the late 19th century by blending Spanish and African musical traditions. Its defining ingredients include the tres, a small Cuban guitar, layered percussion, call-and-response singing, and the clave rhythm. These elements gave son both its distinctive groove and its adaptable structure.

The style reached Havana around 1909, and early recordings followed in 1917. During the 1920s, the sextet became a common ensemble format; by the 1930s, many groups had added trumpets, and larger conjunto bands later incorporated congas and piano.

Salsa emerged much later as a commercially labeled style, particularly in New York during the 1960s, among Cuban, Puerto Rican, and other Caribbean communities. It drew heavily on son cubano and son montuno while also absorbing mambo, rumba, cha-cha-chá, jazz, and other influences. Rumba, cha-cha, and mambo shaped salsa too, but Cuban son is the central foundation named by this question.