When Ashoka died in 232 BC, Mauryan hold on the Indus began weakening. Other Empires tried to retake control of the Ganges heartland though the Shunga revolt. As such, the Mauryans began retreating out of the Indus back east towards Pataliputra (Patna) to protect the imperial capital. This left most of the Indus Valley unguarded and most importantly left the Khyber Pass open to invasion. In 250 BC, the eastern part of the Seleucid Empire broke away to form the Greco-Bactrian Kingdom by Diodotus of Bactria. In 230 BC, Euthydemus overthrew Diodotus to establish himself as king, firmly establishing a Hellenistic kingdom in northern Afghanistan and Tajikistan, distinct from the neighbouring Seleucid Empire. The Greco-Bactrians were allied with the Mauryans and had kept close relations with Ashoka.