Sindh was conquered by the Persian Achaemenid Empire in the sixth century BC. In the late 300s BC, Sindh was conquered by a mixed army led by Macedonian Greeks under Alexander the Great. The region remained under control of Greek satraps only for a few decades. After Alexander's death, there was a brief period of Seleucid rule, before Sindh was traded to the Mauryan Empire led by Chandragupta in 305 BC. During the rule of the Mauryan Emperor Ashoka, the Buddhist religion spread to Sindh.
Mauryan rule ended in 185 BC with the overthrow of the last king by the Sunga Dynasty. In the disorders that followed, Greek rule returned when Demetrius I of Bactria led a Greco-Bactrian invasion of India and annexed most of northwestern lands, including Sindh. Demetrius was later defeated and killed by a usurper, but his descendants continued to rule Sindh and other lands as the Indo-Greek Kingdom. Under the reign of Menander I many Indo-Greeks followed his example and converted to Buddhism.