We never stopped declaring war; declarations of war don't require particular magic words; the Afghanistan and Iraq AUMFs, for instance, were each valid conditional (and, in the former case, broadly open-ended) declarations of war.
> When in the last 30 years did the US Congress declare an act of war?
The grandparent post is a single sentence and identifies two instances that answer that question (they aren't a full answer because there are more examples in that timeframe.)
