An interstellar war involves a warfare between combatants from different planetary systems. The concept provides a common plot device in science fiction, especially in the space opera subgenre. In contrast, the term intergalactic war refers to war between combatants from different galaxies; interplanetary war refers to war between combatants from different planets of the same solar system.
Michael H. Hart argued that if humans ever spread to other planetary systems, the actual likelihood of interstellar war would be low due to the immense distances (and hence travel times involved)–interstellar war would require a vastly greater investment of time and resources than present-day intraplanetary wars involve. By contrast, Robert Freitas argued that the energy expenditure required for interstellar war would be trivial from the viewpoint of a Type II or Type III civilisation on the Kardashev scale.
The earliest fictional references appear to deal with interplanetary, not interstellar war (e.g. H. G. Wells' 1898 novel The War of the Worlds).[original research?] Now that the other planets of the solar system are believed to be devoid of intelligent life, sci-fi writers generally posit some form of faster-than-light drive in order to facilitate interstellar war. Writers such as Larry Niven have developed plausible interplanetary conflict based on human colonization of the asteroid belt and outer planets by means of technologies utilizing the laws of physics as currently understood.
Interplanetary war in fiction can reveal contemporary mores. In general, older fiction relates to the colonial systems of politics and economics of the late 19th and early 20th centuries; mid-20th century depictions often show a heavy influenced from the Cold War and are barely concealed allegories of the conflict between the "free world" and the Communist states, with humans (personified by 1950s-style American archetypes) as the "good guys" and aliens as the "bad guys". Modern fiction often uses the conflict to explore known failings in the human (especially Western) perspective.[original research?]
...interstellar wars will be extremely rare, much rarer than warfare has been on Earth. This will be a consequence of the enormous distances between the stars and large travel times between civilizations... a typical civilization might be involved in a major war only once in 50,000 years, perhaps much longer.