Generally considered to be one of the more unjust wars in human history. The third of the Punic Wars between Carthage and Rome took place in 149 BC, mainly due to Roman resentment over the damage Hannibal wrought during the Second Punic War. The hysteria reached such a fevered pitch that the great statesman of rome, Cato, reputedly ended all his speeches (no matter the subject) with the line "Carthago Delenda Est!" (Carthage should be destroyed).
The actual war itself occured because the Carthaginians were gaining back much of the wealth they had lost in the earlier wars, though very little of their previous power. The Roman senate demanded that the city of Carthage be moved inland, away from the sea, thereby losing all its trade. Carthage refused, though they lacked the military might to openly defy Rome. Rome declared war on this pretext, which is what they were aiming for all along, and laid seige to Carthage. When the city was taken, the inhabitants were systematically murdered, with the survivors sold into slavery. The city itself was demolished, and the ground sown with salt so that nothing would ever grow there again.
Ironically, a city was later erected on the same site and became a full member of the Roman Empire. A citizen of the area formerly known as Carthage eventually became Emperor of Rome.