Peace was the absence of war.
In 1938, after British Prime Minister Neville Chamberlain sought to defuse the Czechoslovakia crisis, (PROSE: Illegal Alien) he declared there would be "peace in our time", but he would be proved wrong. (PROSE: One Wednesday Afternoon) His opponent, Adolf Hitler claimed to be a man of peace before Germany invaded Poland in 1939, as part of a propaganda campaign to paint Warsaw as the true aggressor. (PROSE: Timewyrm: Exodus)
In the Buddhist religion, peace was represented by the swastika. Although the swastika was appropriated by the Nazis during World War II, Buddhists continued to use it as a peaceful symbol after the war. (PROSE: Utopia)
The Eleventh Doctor echoed Neville Chamberlain, claiming "peace in our time" when he and the Tenth Doctor organised a human/Zygon peace conference. (TV: The Day of the Doctor) The negotiated peace proved fragile. (TV: The Zygon Invasion/The Zygon Inversion)
Hecuba challenged the Second Doctor to a game in which players had to imagine ways of defeating their opponents' increasingly destructive weapons. The Doctor brought the game to an end by declaring peace, much to Hecuba's disappointment. (AUDIO: The Queen of Time)