“the king of the north.” This is Antiochus III the Great. In the wars between Antiochus III and Ptolemy V Epiphanes, the army of Antiochus engaged the southern army led by Ptolemy’s general Scopas who eventually ended up in the fortified city of Sidon. But after a siege, Antiochus took Sidon in 198 BC and Scopas surrendered. This victory resulted in Antiochus controlling Palestine down to Gaza, as well as Phoenicia and even some areas on the coast of Asia Minor (now Turkey) that had been under Ptolemaic control.
“the forces of the south will not stand.” This seems to refer to the fact that Egyptian forces sent north to support Scopas at Sidon failed to turn the tide of the war and thus give the Ptolemaic general the victory.