 Complete the following phrase:  A now-independent and warlike Sogdiana formed a border region insulating the Achaemenid Persians from the nomadic Scythians to the north and east. It was led at first by Bessus, the Achaemenid satrap of Bactria. After assassinating Darius III in his flight from the Macedonian Greek army, he became claimant to the Achaemenid throne. The 