The Cold Peace was a political disaster which occurred on Earth in the early 2100s.

The disaster forced a large group of refugees to leave the Sol system and eventually establish the first extra-solar Human colony on the fourth planet of the 70 Ophiucus star system. (TOS novelization: "Miri")

The version of events given in the novelization differs greatly from the episode broadcast. In the novelization, Miri's homeworld was a colony established 500 years before the episode (2100s - 500=16th century?), instead of the duplicate Earth established in the episode and spin-off media, including The Cry of the Onlies.