When Solomon married Pharaoh's daughter, Gabriel descended and stuck a reed in the sea, which gathered a sand-bank around it, on which was built the great city of Rome.When Jewish leaders did something wrong - in this case moral weakness, because Solomon had too many wives, and was not meant to marry gentiles - the Jewish people were said to be punished by God. So Isaac thought that in this case the punishment was to create a great enemy, Rome, which would of course one day bring about the end of Israel - first Rome incorporated into her empire, then she destroyed the Temple.
It raises a few historical questions. We know that Rome was traditionally founded in 753 BC, though archaeological evidence suggests some habitation before this date. We have no idea when Solomon lived, but during the 10th century BC seems to be current wisdom.
More importantly whether an Egyptian pharaoh would have allowed his daughter to marry a foreign king has been questioned - for example see this discussion.