Perhaps he sought to strengthen himself against his enemies in Egypt by an alliance with his powerful neighbour.

At all events, the King of Israel allowed his army to march through Palestine as far as Gezer.

The Egyptians flattered themselves that they had thereby asserted their old claim to sovereignty over Palestine, but the substantial gainer was the Israelitish monarch.

He won the last independent Canaanite city without effort or expenditure, and was allowed to marry into the Solar race.
Shishak had no need of Israelitish alliances.

On the contrary, Solomon was connected by marriage with the dethroned dynasty, and the power of Israel, if unchecked, was a menace to his own kingdom.