Solomon married the daughter of the king of Egypt (3:1). In doing this he followed his father in indulging his lust to gain a Gentile wife.
This was the breaking of the separation of God's holy people from the people of Satan's cosmos—the evil world.
In marrying the daughter of the king of Egypt, Solomon was not regulated and restricted by the law of God. In Exodus 34:16, Deuteronomy 7:3, and Joshua 23:12 God charged Israel not to marry the Gentiles, because the Gentiles would cause them to worship idols. But Solomon openly broke this ordinance of God.
In this matter Solomon was disobedient to God in carrying out God's economy. God's economy included wiping out all the idol-worshipping Gentiles in the land. It was therefore not reasonable for Solomon to marry the daughter of a Gentile king.
Solomon's marrying an Egyptian was a sign of indulgence in the lust of the flesh.
Solomon's marriage to an Egyptian also laid a foundation for his future fall in corruption and ruin.