In 323 BC, the Seleucid Empire was founded by Seleucus I Nicator, a general of Alexander the Great. Stretching from Syria to the Indus River and comprising most of Alexander's realm, the Seleucid state was the most powerful of the Diadochi kingdoms that sprang up after Alexander's death. Quickly however, the Seleucids ran into trouble trying to maintain such an extended realm, facing constant warfare against the other Hellenistic states in the west and with unrest amongst their Iranian peoples in the east.