(1) A preceding event, state, or cause. (2) One's ancestor or parent.
Example:
The harsh terms of the treaty that ended World War I are often said to have been antecedents of World War II.
Antecedents can be persons, conditions, or events that are responsible, if only in part, for a later person, condition, or event. So the rhythm-and-blues music of the 1940s and 1950s is an antecedent of today's rock and roll. And the breakup of the Soviet Union was surely an important antecedent of the war in Yugoslavia. Since our parents and ancestors are responsible for our existence, they are our own antecedents.