Interstellar war

During the Sontaran invasion of Earth, the Tenth Doctor noted that for Earth to launch nuclear missiles against the Sontarans would have started an interstellar war. (TV: The Poison Sky)

According to the Seventh Doctor, Earth was involved in an interstellar war in the 27th century, which was ended by a peace treaty that was drawn up thanks to a Haitian who first deciphered the Rihanssu language. (PROSE: The Pit)