The Second Diadoch War was triggered by the death of Antipater, the regent of Alexander the Great’s empire. His death was probably always going to trigger a new round of conflict, but his choice of successor virtually guaranteed it. Rather than appoint his son Cassander, who he felt to be too young, Antipater selected another of Alexander’s former generals, Polyperchon.
Cassander was suitably offended by this choice, and travelled to join Antigonus, commander of the Macedonian armies of Asia and satrap of large parts of Asia Minor. In the aftermath of the First Diadoch War, Antigonus had been given the task of defeating Eumenes of Cardia. Antigonus had pushed Eumenes back to Nora, in Cappadocia, and was conducting a siege of that fortress. Cassander’s arrival triggered Antigonus’s own ambitions. He abandoned the siege of Nora after apparently converting Eumenes to his side, and formed an alliance with Cassander, Lysimachus (satrap of Thrace) and Ptolemy, already the virtually independent ruler of Egypt. Polyperchon’s only senior ally in the upcoming conflict would be Eumenes, who soon reverted to his normal loyalty to the Macedonian royal family.
There is some disagreement as to dating of the events of the Asian part of this war. Thus the battle of Paraetakena is dated to either 317 or 316 BC, the death of Eumenes to 316 or 315. For simplicity I will be adopting the dating scheme used by the Cambridge Ancient History (2nd Edition), which tends to favour the earlier dates.
Fortunately this disagreement on dates has little impact on the narrative of the war. The Second Diadoch War was essentially two wars, one in Greece between Polyperchon and Cassander, and one in Asia between Eumenes and Antigonus. This separation was made more complete in 318 BC, when Antigonus defeated a loyalist fleet at the battle of the Bosporus.
The war in Asia is the easier to follow. Eumenes was forced out of Asia Minor into Phoenicia, where he planned to build a fleet. Antigonus pushed him out of Phoenicia towards Persia, where the two men fought at least two major battles, at Paraetacene in 317 and Gabiene in 316. Eumenes could claim a slight victory at Paraetacene, and a draw at Gabiene, but despite that he was betrayed by his own soldiers after Gabiene, handed over the Antigonus and executed.
Further south Ptolemy invaded Syria, intending to secure his borders. He was unable to hold on to his conquests at this time, but his actions are widely seen to indicate that he was already acting as an independent ruler of Egypt rather than as one of the rivals for the rule of Alexander’s empire.
The war in Greece and Macedonia was more complex. Polyperchon made an attempt to win support in Greece by promising to restore the liberties of the Greek cities. This briefly won him the support of Athens, but Cassander soon expelled him from that city, imposing his own form of government on that city in 317. Polyperchon was soon restricted to the Peloponnese.
While he was struggling in the south, back in Macedonia a dynastic bloodbath unfolded. In an act that must have been inspired by desperation, Polyperchon had invited Alexander’s ruthless mother Olympias back from virtual exile. She appeared on the border of Macedonia later in 317, at the head of an army. She then captured and murdered Alexander’s half brother Philip III Arrhidaeus and his wife Eurydice. Her purpose in this was to secure the succession for her grandson Alexander IV.
Her actions had the opposite result. Cassander invaded Macedonia, where Olympias had alienated all possible supporters. She was condemned by the Macedonia army, and then besieged in Pydna (217-216 or 215 BC). Olympias was finally starved out, and executed by the families of her victims.
The Second Diadoch War ended with Antigonus in command of most of Alexander’s Asian conquests, Ptolemy ruling in Egypt and Cassander in Macedonia. The only remaining member of the Macedonian royal family was Alexander the Great’s infant son Alexander IV, who was unlikely to let him reach adulthood.
The Second Diadoch War was followed almost immediately by the Third. This time it was Antigonus who triggered the fighting in an attempt to unit Alexander’s empire under his own rule.