Alexander's successors (Diadochi) were a group of generals who fought for control of his empire after his premature death in 323 bc. They were, with the exception of Eumenes, drawn from the Macedonian military aristocracy. All had fought under Alexander; they were ruthless and veteran military leaders. Prominent among them were Antigonus ‘the One-Eyed’ and his son Demetrius Poliorcetes—whose descendants would become kings of Macedon—Lysimachus, Antipater, Cassander, Polyperchon, Ptolemy—later king of Egypt—and Seleucus—founder of the Seleucid dynasty which came to control the Syrian and Iranian parts of the Alexandrian empire.
The wars these men fought fell into four main phases. First, in the immediate aftermath of Alexander's death a series of confused campaigns were fought as numerous generals jockeyed for position. Secondly, Antigonus and Demetrius fought an extensive and successful campaign for control of Syria and Mesopotamia against Eumenes which culminated in the battles of Paraitakene (317 bc) and Gabiene (316 bc). Thirdly, Greece and western Asia Minor were the scene of interminable conflicts dominated by small actions and sieges, in which Cassander and Polyperchon were eliminated from the contest. Finally, Seleucus and Ptolemy put paid to Antigonus' dreams of reuniting the empire under his leadership at Gaza (312 bc) and the decisive Ipsos (301 bc). These wars set the political scene in the Hellenistic east until the conquest of the region by Rome, Greece divided between competing city states and leagues and three large Macedonian-dominated monarchies, Macedon, Egypt, and the Seleucid empire.
Militarily developments saw the Macedonian style of war based on the long-spear-armed phalanx and aristocratic lance-armed charging cavalry reaffirmed as the dominant tactical system of the eastern Mediterranean and Near East. Added to it were certain native traditions—such as missile armed infantry and cavalry—and the widespread use of the elephant. The size of armies grew rapidly in response to the military needs of the combatants; they were, however, unreliable and battles were often decided by cavalry actions on the flanks, as at Gaza and Ipsos, where infantry centres surrendered once outflanked. There were also major developments in fortification with the rapid evolution of larger and more complex defences for cities and fortresses. In response siege technology leapt forward with the development of ever larger and more effective equipment, such as mobile towers and catapults.
— Stephen Nutt
