The Xi'an-Human Cold War was a period of military and political tension between the United Empire of Earth (UEE) and the Xi'an Empire. It was sparked from the events surrounding first contact between the two civilizations in SEY 2530 (MXY III.838), when the Xi'an military arrested Human workers from a terraforming company that tried to set up operations on a planet in the Xi'an-controlled Th.us'ūng system.

Although the hostages were eventually released unharmed, an arms race began, and bordering planetary systems became militarized zones known as the Perry Line. When Ivar Messer I reorganized the government after the First Tevarin War and ascended as the first Imperator for life, he and his descendants exacerbated hostilities by blaming all problems in the UEE on Xi'an subterfuge.

Relations only began to thaw in SEY 2789 (MXY III.1040) when Senator of Terra (Terra III)Terrence Akari and the young Xi'an EmperorT.uēng se Kr.ē secretly signed a non-aggression treaty. In SEY 2793 (MXY III.1044), after the events of the Anti-Messer Revolution, the Cold War finally came to a formal end with the signing of the Perry Line Pact.