What does Daniel 11:5 mean?

As part of a prophecy delivered to Daniel (Daniel 10:1; 11:2), an angelic being has mentioned the four kings who would eventually replace Alexander the Great (Daniel 11:3–4). History confirms these predictions, which were given in 536 BC and not fulfilled until some two hundred years later. Alexander died in 323 BC without an heir. His conquered territory was split among four of his generals: Lysimachus, Cassander, Ptolemy, and Seleucus (Daniel 7:6; 8:5, 8). In this verse, the "king of the south" is described in ways consistent with historical records about Ptolemy.

Ptolemy I Soter initially received authority over the territory of Egypt in 323 BC. Seleucus I Nicator was one of his "princes." In 321 BC, Seleucus was appointed over Babylon. Five years later, he was challenged by another of Alexander's former military leaders. Ptolemy successfully aided Seleucus, his former subordinate; as a result, Seleucus controlled a much larger territory than even Ptolemy, including Syria and Media. This corresponds to this verse which predicts the "prince" will become stronger than the "king of the south."