Medals as a form of award and recognition for military service dates back to the time of the Roman Republic (509-27 BC), with this tradition spreading across the world and still being preserved today. Medals are generally awarded for periods of service or completion of campaigns, whilst decorations are reserved for specific achievements. During the Vietnam War (1955-1975), medals were distributed by North Vietnam, South Vietnam, the United States, Australia and New Zealand. Amongst these was the Medal of Honor, the highest military medal in the United States which has been awarded since the American Civil War for remarkable acts of bravery; the Bronze Star was also bestowed upon soldiers for both heroism and merit. Like many other military awards, Vietnam medals have become collectors' items and are sold by dealers and at auction.