In 1989, in an alternate timeline created by the Elder Gods in the hope of destroying Earth, the Western powers' satellites detected a Soviet army amassing on the border of West Germany, which was destroyed by an American tactical nuclear weapon.
On the same day, the Parliament of the United Kingdom passed the Emergency Powers Act, which resulted in all airports being closed and all hospitals being cleared of non-critical patients to make room for expected casualties. Anti-war protests took place in London, Manchester and Liverpool, which led to rioting and looting and the imposition of a curfew in all cities in the UK.
World War III broke out three days later. Given that nuclear weapons were used by both sides, hundreds of millions of people were killed in the conflict. This timeline was ultimately negated by the Seventh Doctor. (AUDIO: Protect and Survive)