Thebes’ victory at Leuctra allowed it to attract allies and wield influence in many parts of the Greek world. It moved quickly from a position of relative weakness to become a leading power in Greek inter-state politics, acting in central Greece, Thessaly and Macedon, the Peloponnese, and – briefly – the Aegean. The available evidence of Theban activity in these various regions is very uneven. Information is richest on events in the Peloponnese, because Xenophon, who gives the fullest ancient account of the 360s, concentrates on Peloponnesian affairs to the neglect of other parts of Greece. Even on Peloponnesian affairs Xenophon is partisan in his judgments, both political and social, and also omits major events of the first importance, such as the liberation of Messenia. None the less his account, taken in conjunction with other available evidence, offers a quantity of information on Peloponnesian affairs that we do not possess for other areas. Much remains uncertain even in Peloponnesian history, but even more in the history of other Greek areas in these years.

The opportunities which opened up for Thebes in the aftermath of Leuctra were great and tempting, but not all predictable. In the Peloponnese Sparta had for long done what it could to prevent unwelcome change. Resentment had none the less developed among Peloponnesian states on a great number of issues; some of these were particular matters, such as Elis’ claim to Triphylia and Mantinea's desire to refound her urban centre, while others were wider, such as a wish to create an Arcadian federal state.

The main acts of Nicaea were gradually reversed over the years 327-60. Constantine honored its name and canons throughout his life, but recalled Arius from exile, leaned on church leaders to restore him to communion, and sidelined Arius’s opponents. Constantius II flouted Nicaea’s canons and officially replaced its creed. Nonetheless, Nicaea’s pronouncements on the Son’s relationship to the ousia of the Father, including the term homoousios, which had been a response to Eusebius of Nicomedia’s Letter to Paulinus of Tyre, continued to be debated throughout this period in a succession of mutually allusive theological works. These include Eusebius of Caesarea’s Letter to his Church, Eustathius of Antioch’s Against the Arian Madness, Asterius the Sophist’s Defence of Eusebius of Nicomedia, Marcellus of Ancyra’s Against Asterius, Eusebius’s Against Marcellus and On Ecclesiastical Theology, Acacius of Caesarea’s Against Marcellus, Marcellus’ Letter to Julius of Rome, Athanasius’s Orations Against the Arians, the Profession of Faith of Sirmium 351, and Athanasius’s On the Decrees of Nicaea. The last of these, together with his formidable political skills, established the Nicene Creed against all the odds as the only formula which was able to command widespread support among bishops across the empire after the death of Constantius.