Complex sentence: Thus a period of reconciliation began which facilitated a close relationship between the Persians and Medes, and the capital of the Median province to passed to the Persians as one of Persia's capitals in their newly formed empire.
Split into simpler sentences: Thus a period of reconciliation began, which facilitated a close relationship between the Persians and Medes. And enabled the capital of the Median province to passed to the Persians as one of Persia's capitals in their newly formed empire.