Sefer Nachum (Nahum) is the book of the vision of Nachum of Elkosh, a navi (prophet). It is the prophecy concerning Nineveh, the great city of Ashur (Assyria) (1:1). It is one of the Trei Asar (the Twelve), the twelve short books of the Neviim Acharonim (the Later Prophets), which the Gemara (Bava Batra 14b) says are written together as one sefer.
Perek 1 describes Hashem's power and judgment. Hashem is slow to anger, but He does not clear the guilty, and before Him the sea dries up and the mountains shake. He is a stronghold on the day of trouble for those who trust in Him. Hashem promises Yehudah (Judah) that He will break the yoke of Ashur off its neck, and He decrees that the name of Yehudah's enemy will not go on and that his idols will be cut off.
Perek 2 opens with a messenger on the mountains announcing shalom (peace), and Yehudah is told to celebrate its festivals and pay its vows, because the wicked enemy will not pass through it again. Then the navi describes the attack on Nineveh, with red shields and racing chariots. The river gates open, the people flee and the city's treasures are plundered. Nineveh, which filled its dens with prey like a lion, is left empty.
In perek 3 Hashem condemns the city of bloodshed, full of lies and plunder, which led nations astray with its sorceries. He will expose its shame before the nations. Nineveh is no stronger than No-Amon, which also had rivers and allies and still went into exile. Its forts will fall like ripe figs, its merchants and officials will vanish like locusts, and the people of the king of Ashur will be scattered on the mountains. All who hear of Nineveh's fall will clap their hands over it, because its cruelty has reached everyone.
Sefer Nachum has three perakim.