Ireland, was the place that Vikings raided most often.
Silk, common currency, fireworks.
Those are the main three I know of.
The Vietnam War usually has a negative legacy in the eyes of American citizens. This war caused the lives of thousands of US soldiers and involved hundreds of millions of dollars spent by the federal government. Many citizens did not agree with/understand why we were putting so many resources into a country that was thousands of miles away. This resulted in hundreds of protests across the US.
Along with the "waste" of resource/soldiers, citizens also disliked the way in which the US government used tactics that resulted in the deaths of innocent civilians. The use of Agent Orange was a perfect example, as this herbicide had detrimental health effects on thousands of innocent Vietnamese citizens.
The correct answer is a the prohibition of alcohol
It didn't stick however, and now, the 18th amendment is not in use anymore and alcohol is legal.