Albert Barnes Commentary 1 Kings 14:25

"And it came to pass in the fifth year of king Rehoboam, that Shishak king of Egypt came up against Jerusalem;" — 1 Kings 14:25 (ASV)

The examination of the famous inscription of Shishak at Karnak has proven that the expedition it commemorates was directed against Palestine. This discovery has also shed considerable light on the relationship between the two kingdoms at that time.

Of the fifteen fortified cities Rehoboam established early in his reign (2 Chronicles 11:5–12), three—Shoco, Adoraim, and Aijalon—are distinctly mentioned among Shishak’s conquests. Other towns in Judah and Benjamin also appear on the list.

Furthermore, a significant number of the captured cities were in Jeroboam's territory; these cities are described as "either Canaanite or Levitical." From this, we can gather that during the four years immediately following the separation of the kingdoms, Rehoboam retained a powerful hold on his rival's dominions. Many Canaanite and Levitical towns acknowledged his sovereignty and held out against Jeroboam, who likely called in Shishak mainly to assist him in compelling these cities to submit. The campaign was completely successful.