After the Decade of Anarchy, the organization of the Caliphate changes. The caliphs remain in Baghdad, but the provinces are ruled by dynastic emirs (rather than rotating governors). We’re starting our tour through the emirates, moving from East to West, before we return to the ‘Abbasids.
The Tahirids were governors of Khurasan, but they serve as a good starting point to understand dynastic power in the East. However, after the middle of the 9th century, these families hold more power. They’ll continue to acknowledge ‘Abbasid authority, but we see regionally-specific developments such as the rise of New Persian literature in the courts. This has led some people to look to these eastern emirates as a locus of “Iranian” nationalism, an idea that is anachronistic.