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Why did Ptolemy I Soter fight Antigonus I Monophthalmus?
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Ptolemy I Soter
Ptolemy I Soter, portrait on a silver tetradrachm; in the British Museum
Ptolemy I Soter fought Antigonus I Monophthalmus primarily because of the intense power struggle among the diadochi (successors) following the death of Alexander the Great.1
The conflict was driven by the following factors:
- Opposition to Hegemony: Antigonus sought to reunite Alexander’s empire under his own rule. Ptolemy, along with other successors like Seleucus I Nicator, Lysimachus, and Cassander, formed coalitions to thwart his expansionist ambitions and maintain their own regional power bases.12
- Territorial Disputes: Antigonus’s control over vast territories in Asia Minor, Syria, and the Near East threatened the autonomy of the other successors. Ptolemy specifically engaged in military campaigns against Antigonus to protect his interests in Egypt and the eastern Mediterranean, such as his attack on Cilicia and the battle at Gaza.2
- Collective Security: After Antigonus invaded Egypt in 306 BCE, the other successors recognized the necessity of offering concerted resistance to prevent him from dominating the entire empire. This culminated in the alliance that defeated Antigonus at the Battle of Ipsos in 301 BCE.12