By David K. Johnson, Ph.D., King’s College
In some cases, war is seen as justifiable. War theory is seen as the middle ground between militarism and pacifism. The theory also includes what things and actions in war can be considered justified or justifiable. But are there certain actions in war that cannot be justified?

The Laws to Begin War
War theory is rooted in the writings of St. Augustine, who lived in the 5th century. He was trying to reconcile war with Jesus’ pacifism. It was later expanded by Thomas Aquinas. The conditions under which war is justified are generally divided into two categories by Latin phrases, jus ad bellum and jus in bello.
Jus ad bellum, what we might call, “the laws to war,” dictates the conditions under which going to war is justified. War must be declared by a legitimate authority—say, a leader elected by the population going to war. The war must also be for a just cause; personal jealousy, pride, or lust for power won’t cut it. Neither would revenge.
You must aim to do the minimum amount of harm necessary. And you must have the intention to achieve a just cause, be reasonably sure of victory, and you must only engage in war as a last resort.
This is a transcript from the video series Sci-Phi: Science Fiction as Philosophy. Watch it now, on Wondrium.
The Laws to Conduct War
Jus in bello, or what we might call “the laws of war,” dictate how war must be conducted if it is to be justified. Military actions must be rightly intended for legitimate military targets or objectives, and must also be proportional. They can’t do more harm than good, and must do the minimum harm necessary to accomplish the objective.
They must be both necessary and sufficient for that objective—you shouldn’t be able to accomplish the same goal in a nonviolent way, and what you do must be enough to accomplish it. They must also be approved by a legitimate authority. And finally, they must discriminate between combatants and non-combatants; they cannot intentionally target civilians.

Violation of Rules
It’s important to note that these are essentially guidelines; what counts as a “just cause,” for example, is debatable. And whether a war is just or not is a matter of degree. A violation of one of the principles—like the existence of a rogue officer like Colonel Kurtz in Apocalypse Now—doesn’t necessarily make the war completely unjustified.
What’s more, if one soldier sees another using disproportionate means, he is not morally obligated to abandon the war because the entire war is now unjust. To make sure we understand how to apply the criteria, let’s apply them to some sci-fi wars.
Learn more about Thomas Aquinas.
War Theory in Starship Troopers
Interestingly, war theory is actually alluded to in the film. As the humans are about to go to war with the bugs, a reporter says: “Some say the bugs were provoked by human attempts to colonize within the [Arachnid Quarantine Zone], that a ‘live and let live’ policy is preferable to war with the bugs …” But he is immediately shouted down by Johnny. “Yeah, well, I’m from Buenos Aires, and I say kill ’em all!”
In light of this, it seems their war is unjustified. Yes, the bugs attacked them, but the humans colonized their territory. Peace could have been brokered by a treaty or pulling the colonists out. The humans also entered the war without good reason or strategy, only to be slaughtered on Klendathu.
In addition, their plan to “kill ’em all” is disproportionate to the good they mean to accomplish. It’s not like the bugs actually could wipe out the entire human race. They’re not even capable of space travel, and Earth now has a defense against their asteroids that the insectoids are sending. At this point, as Johnny makes clear, the war is only about revenge—which is not a just cause.
The Ender’s Game Scenario
How about the war waged in Ender’s Game? Earth has been attacked by an alien race called the Formics. To prepare to attack their home world, the military is training children, and a young genius named Ender is at the top of their list. He accelerates through training, which involves a series of “games”—simulated battle scenarios.
In his final game, he commands the entire fleet in an attack on the Formics’ home world. He manages to fire a Molecular Detachment Device, at the cost of large portion of his fleet, thus annihilating the entire Formic race. The big reveal, of course, is that this final test wasn’t a game; he was actually commanding the fleet remotely and just sacrificed thousands of humans to commit genocide.
The Unconsidered Options

Was this war justified? One might argue that the genocide of the Formic race was justified because genocide was their intention regarding us. But, on just war theory, one cannot be motivated by the “eye for an eye” principle. One must never use more force than is necessary to achieve the desired goals.
As Ender points out, “The way we win matters.” Wiping out the entire Formic race was not necessary to prevent another attack. Indeed, it would seem that genocide is never necessary for any morally worthwhile goal, and thus is always unjustified.
Learn more about war stories in science fiction.
The Unwritten Rules of War
It also seems that the humans in Ender’s Game never even considered a nonviolent solution. At the end of the movie, Ender realizes that the Formics had been trying to communicate with him; yet communication was never even attempted by the humans.
Ender’s Game might actually also reveal a law of war that we need to add: the soldiers must know they are killing. After all, St. Augustine couldn’t have anticipated the possibility that someone could be tricked into thinking an actual war was really a game.
Common Questions about War Theory and Science Fiction
Some just causes for declaring a war are: it must be declared by a legitimate authority—say, a leader elected by the population going to war. The war must also be for a just cause; personal jealousy, pride, or lust for power won’t cut it.
After Ender wins the final “game” in which he sacrifices most of his fleet to wipe out the alien Formics, it is revealed that it wasn’t a game. Ender had actually been commanding the fleet remotely and had just sacrificed thousands of humans to commit genocide against another race.
Ender’s Game might actually also reveal a law of war that we need to add, especially in the digital age: the people waging war must know they are really fighting a war and killing others.