A dire vision is declared to me: The prophet makes Babylon's experience personal, which strengthens his poetry. The concise language and repeated sounds, like The traitor still betrays (Hebrew habboged boged) and the destroyer still destroys (Hebrew hashoded shoded; also in Isaiah 33:1), add to this effect.
The Elamites lived northeast of Babylon. They, along with the Medes, were major rivals of the Babylonians.
I will put an end to all her groaning: Babylon caused suffering by attacking and enslaving many nations. The Elamites and Medes likely helped overthrow Babylon in 539 BC (Isaiah 21:9).