The victory at Corupedium has given Seleucus,…

…Byzantium, and …

The formidable task of holding together the empire falls to the son and successor of Seleucus on his father's assassination in 281 BCE.

Antiochus entombs his father's ashes in Seleucia, initiates (probably) the posthumous cult of his father, and orders his veneration as Zeus Nicator.

He is soon compelled to make peace with his father's murderer, Ptolemy Keraunos, apparently abandoning Macedonia and Thrace.

In Anatolia he is unable to reduce Bithynia or the Persian dynasties that rule in Cappadocia.

Antiochus is immediately beset by revolts in Syria (probably instigated by Egypt) and by independence movements in …

…northern Anatolia, whose states (led by Heraclea, …

…Bithynia, and …

…Pontus), form a league against the Seleucid king.

Pontus, with its capital at Amaseia (modern Amasya) established at the end of the fourth century in the wake of Alexander's conquests, is superficially Hellenized, but the kingdom retains its Persian social structure, with temple priests and Persianized feudal nobles ruling over a heterogeneous village population.

Seleucus, seeing an opportunity to intervene for his own gain in the politics of both Lysimachan Thrace and Ptolemaic Egypt, prepares an expedition against Lysimachus, personally leading an army from Syria.

The two armies meet in 281 at Corupedium, near Sardis, in Lydia.

Almost nothing is known about the battle itself save that Seleucus won.

According to Memnon of Heraclea's History of Heraclea Pontica, Lysimachus was killed by a javelin thrown by Malacon, a Heracleian soldier serving under Seleucus.

Seleucus’ army routs the Macedonian forces.

With the death of Lysimachus and the capture of Thrace, his queen flees to Macedonia.

Antigonus although possessed of only a few bases in Greece after Seleucus' murder in 281, lays claim to Macedonia, which Antiochus disputes.

The expansionist Roman Republic, on the ascendant in the early third century BCE, has spent the 280s suppressing unrest in northern Italy, but Roman attention is soon directed to the far south as well by a quarrel between the Greek city of Thurii and a Samnite tribe.

Thurii calls upon the assistance of Rome, whose naval operations in the area provoke a war with …

…the Greek city of Tarentum in Apulia.

Rome had violated a treaty by sending ships into the Gulf of Tarentum, only to have them sunk by the Tarantine fleet.

As in previous conflicts with Italian peoples, Tarentum summons military aid from mainland Greece, calling upon Pyrrhus of Epirus, an able general who has consolidated the Epirote monarchy and warred successfully with his eastern neighbor, Macedonia.

The continuous troubles in the west cause Seleucid control in the far eastern part of the empire to weaken.

Antiochus makes his eldest son king in the east in 280, but he proves incompetent.