Verse 1 blatantly identifies Nahum as the author. Only modern, anti-supernatural scholars argue for a post-exilic author, but this theory has no grounding outside of secularist biases.
God will bring judgment upon Nineveh (and the Assyrian Empire) because of the wickedness that they have committed.
Nothing is known of Nahum outside of what is written within this text. He came from the city of Elkosh, and although its exact location is unknown, it was certainly within Judah. The book was likely written around 650 BC. Evidence for this date is as follows. Nineveh fell in 612 BC to the coalition of rebels against the Assyrians. Nahum clearly speaks about this event as being in the future, so it must have been written before 612. Also, Thebes in Egypt was sacked by the Assyrians in 663 BC, which Nahum references as having already occurred (3:8). We can also assume that Nahum was writing closer to 663 than 612 because he describes Nineveh as being a mighty force, but Assyria’s power significantly diminished during its final years. Thus, 650 BC seems like a safe assumption.
We must also consider a few more bites of historical context. The Assyrians were a fearsome and ruthless people who established one of the first great empires through advanced siege technology and terror tactics, and Nineveh was the capital. Roughly one hundred years earlier, God sent the prophet Jonah to Nineveh with a message of judgment, but the people miraculously repented and were spared. Unfortunately, their repentance did not last. Around 50 years later, in 722 BC, the Assyrians destroyed Samaria, the capital of Israel, the northern kingdom. The desolation of their brothers was, therefore, still fresh in the mind of Judah, the southern kingdom.
Nahum is essentially a sequel to Jonah. Although Jonah became bitter with God’s mercy toward the people of Nineveh, here we find that God’s patience for them has reached its end. The LORD boldly foretells the total destruction that he is going to bring upon the Assyrians as judgment for their iniquities. Nahum never shies away from the wrath of God but gives vivid and poetic imagery of its coming. Although Nahum seems to bear a significantly different message than Jonah, together they display the great patience and justice of God. Through Jonah, God was willing to give mercy at the repentance of the Assyrians. This repentance, however, was short-lived, and they quickly continued to commit atrocities as they ever expanded their empire. Nahum’s message may seem severe, but it is a message of justice. It is proclamation of hope that the evil will not escape the due wrath of God. In fact, the psalm that opens the book urges us to keep God’s wrath, vengeance, patience, and goodness in the forefront of our minds as we read the remainder of the Nahum’s oracles.