“But his sons will continue the war.” Seleucus II Callinicus had two sons: Seleucus III Ceraunus (ca. 227–223 BC) and Antiochus III the Great (ca. 223–187 BC). They waged war on Ptolemy in Egypt.
“his sons…he…he.” This is very historically accurate. Although the sons of Seleucus II Callinicus started to make war on Ptolemy together, the elder son, Seleucus III Ceraunus, died in a war and the younger son, Antiochus III “the Great” took over. The verse represents this by changing from the plural to the singular.
Antiochus III “the Great” was successful in restoring the territory of Phoenicia and Palestine to Seleucid control as far south as Gaza, which was strong and well fortified, and thus aptly referred to as a “fortress.”