Nahum is devoted to neither Israel (the Northern Kingdom) or Judah (the Southern Kingdom) but Assyria. As recounted in 2 Kings 18-19 and Isaiah 36-37, having conquered the Northern Kingdom of Israel, Assyria attempts to conquer Judah, advancing all the way to the very walls of Jerusalem. Through his messenger, the king of Assyria attempted to persuade Hezekiah and Jerusalem to surrender with a series of arguments wherein the king and Assyria falsely represented God. Hezekiah took Sennacherib’s letter to the temple, spread it out before the Lord and prayed. The Lord answered through Isaiah and the angel of the Lord killed 185,000 Assyrians who returned to Assyria, never to return. Nahum might be though of as God’s own letter back to the Assyrians, who were so proud and boastful claiming not just military and political, but spiritual superiority to Israel and all nations, and that their accomplishments came through their false gods, not the One True God. It wasn’t a political agenda that brought God’s judgment, but spiritual unfaithfulness and rejection of God.