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Rivalry and wars

In 321 BC, Perdiccas attempted to invade Egypt, only to fall at the hands of his own men. Ptolemy's decision to defend the Nile against Perdiccas ended in fiasco for Perdiccas, with the loss of 2,000 men. This failure was a fatal blow to Perdiccas' reputation, and he was murdered in his tent by two of his subordinates. Ptolemy immediately crossed the Nile, to provide supplies to what had the day before been an enemy army. Ptolemy was offered the regency in place of Perdiccas, but he declined. Ptolemy was consistent in his policy of securing a power base, while never succumbing to the temptation of risking all to succeed Alexander.

In the long wars that followed between the different Diadochi, Ptolemy's first goal was to hold Egypt securely, and his second was to secure control in the outlying areas: Cyrenaica and Cyprus, as well as Syria, including the province of Judea. His first occupation of Syria was in 318, and he established at the same time a protectorate over the petty kings of Cyprus. When Antigonus I, master of Asia in 315, showed expansionist ambitions, Ptolemy joined the coalition against him, and on the outbreak of war, evacuated Syria. In Cyprus, he fought the partisans of Antigonus, and re-conquered the island (313). A revolt in Cyrene was crushed the same year.

In 312, Ptolemy and Seleucus, the fugitive satrap of Babylonia, both invaded Syria, and defeated Demetrius I, the son of Antigonus, in the Battle of Gaza. Again he occupied Syria, and again—after only a few months, when Demetrius had won a battle over his general, and Antigonus entered Syria in force—he evacuated it. In 311, a peace was concluded between the combatants. Soon after this, the surviving 13-year-old king, Alexander IV, was murdered in Macedonia on the orders of Cassander, leaving the satrap of Egypt absolutely his own master.

The peace did not last long, early in 310 he was informed that his ally Nicocles of Paphos was planning to defect to Antigonus; he sent some agents, who together with his brother Menelaus, who was still on Cyprus with an army, dealt with the situation, they surrounded Nicocles palace and forced him to commit suicide. In 309 Ptolemy personally commanded a fleet which detached the coastal towns of Phaselis, Xanthos, Kaunos, Iasos and Myndus in Lycia and Caria from Antigonus, then crossed into Greece, where he took possession of Corinth, Sicyon and Megara (308 BC). In 306, a great fleet under Demetrius attacked Cyprus, and Ptolemy's brother Menelaus was defeated and captured in another decisive Battle of Salamis. Ptolemy's complete loss of Cyprus followed.

The satraps Antigonus and Demetrius now each assumed the title of king; Ptolemy, as well as Cassander, Lysimachus and Seleucus I Nicator, responded by doing the same. In the winter of 306 BC, Antigonus tried to follow up his victory in Cyprus by invading Egypt; but Ptolemy was strongest there, and successfully held the frontier against him. Ptolemy led no further overseas expeditions against Antigonus. However, he did send great assistance to Rhodes when it was besieged by Demetrius (305/304). The Rhodians granted divine honors to Ptolemy as a result of the lifting of the siege.

When the coalition against Antigonus was renewed in 302, Ptolemy joined it, and invaded Syria a third time, while Antigonus was engaged with Lysimachus in Asia Minor. On hearing a report that Antigonus had won a decisive victory there, he once again evacuated Syria. But when the news came that Antigonus had been defeated and slain by Lysimachus and Seleucus at the Battle of Ipsus in 301, he occupied Syria a fourth time.

The other members of the coalition had assigned all Syria to Seleucus, after what they regarded as Ptolemy's desertion, and for the next hundred years, the question of the ownership of southern Syria (i.e., Judea) produced recurring warfare between the Seleucid and Ptolemaic dynasties. Henceforth, Ptolemy seems to have involved himself as little as possible in the rivalries between Asia Minor and Greece; he lost what he held in Greece, but reconquered Cyprus in 295/294. Cyrenaica, after a series of rebellions, was finally subjugated in about 300 and placed under his stepson Magas.