The Wizarding War was a period of violence that occurred in magical Britain in the 1970s and until 1981. It was a conflict between Voldemort's Death Eaters and everyone who opposed them, most notably the Ministry of Magic (canon) and the Order of the Phoenix (canon) led by Albus Dumbledore.
The Wizarding War ended with Voldemort's apparent death during his attack on the Potters on October 31st, 1981. October 31st is now Harry Potter Day.