The first Seleucus, by his claim to the sovereignty of Lower Syria, established a ground of constant contention with the Ptolemies; and though he did not prosecute the claim to the extent of actual hostility, yet in the reign of his son, Antiochus I., called Soter, the smothered quarrel broke out.
Soter fomented the discontent of Cyrene with its subjection to Egypt, and made at least one expedition against Ptolemy Philadelphus in person (B.C.

264).

His efforts did not meet with much success; but they were renewed by his son, Antiochus II., surnamed "the God", who warred with Philadelphus from B.C.260 to B.C.250, contending with him chiefly in Asia Minor.

These wars were complicated with others.

The first Antiochus aimed at adding the kingdom of Bithynia to his dominions, and attacked successively the Bythynian monarchs, Zipcetas and Nicomedes I.( B.C.
280-278).