This is still the personified Assyria speaking. He notes that he has been successful in conquering nations. He has founded nations whose "gods" were more powerful that those of Jerusalem and Samaria. We should remember that this king would not know the power of the true God, and so he is using the gods of those nations as representatives of the nations. These are nations of political and economic influence that are greater than Jerusalem or Samaria, and it is on that basis that the comparison is made.
Because he has been successful against more powerful nations, Assyria presumes success against Jerusalem. In this, he is trusting in his own power, and is completely ignorant of the Lord who wields him as a weapon.