Answer
Demetrius II, the Seleucid king, was defeated by Zabinas, a Syrian usurper, in 125 BC. Zabinas had been a slave of Alexander Balas, another Seleucid king who had been overthrown by Demetrius II. Zabina's victory over Demetrius II marked the culmination of a series of rebellions and power struggles within the Seleucid Empire, which had been weakened by the expansion of the Roman Republic and the rise of Parthia.