Why did Pharaoh's army leave Egypt?
Rashi: It was in order to help Yehudah.
Radak: It was to help Tzidkiyah, for he rebelled against Melech Bavel, who made him swear in the name of Hashem when Nebuchadnetzar made him king, and he rebelled. He sent to Pharaoh to help him. When Melech Bavel sent his army [against Tzidkiyah], Pharaoh's army left Egypt.
Why did the Bavliyim go away from Yerushalayim?
Malbim: They did not return to Bavel, just they abandoned the siege, for they feared lest an enemy (Pharaoh, who came to help Yehudah) attack them from the outside, and they will be attacked from in front and in back of (via Pharaoh and Yerushalayim). Therefore, they went to meet Pharaoh and fight him.
