War is defined as being in a state of hostility or rivalry that usually consists of physical force between opposing parties. With this in mind, we must answer the ethical question of whether or not war can ever be morally justified. Surely there are times in which conflict between states and peoples arise out of necessity, but there are also points in which conflicts arise out of needless ambitions, and it's in these instances that war is never justified. The principles of act utilitarianism can be applied in creating a rational, justifiable cause for war. War is sometimes necessary, this is one of the most heralding facets of human existence that we must come to terms with. Not all wars, however, have been fought out of necessity and remain a tragedy of human history. Hindsight has shown us that certain wars have determined the greatest amount of utility for the greatest amount of people. Act utilitarianism implies that we make a binary choice to go to war to protect the lives of the entire nation, or pacify ourselves against aggressive forces, it is essential to go to war.

When dealing with the ethical question of war, we can use some evidence throughout history that has shown us that certain wars have been waged for the greater good of humanity. Most of these wars were fought either to stop international aggression, or fiercely fought battles of defense against foreign invaders:

• WW2 was a necessary war in which arms had to be taken against the Axis powers who had serious ambitions of enslaving the Slavic states of Eastern Europe and spreading Aryan/Japanese supremacy throughout the world.
• When the Union Army marched into the Confederacy in order to restore the Union could be seen as justifiable because it meant the preservation of the country as well as the abolition of slavery.
• After North Korea was split from South Korea, it was a necessity for North Korea to attempt the reunification of the two Koreas to achieve economic and social success for its people.
• The war that has been waged against Israel by Palestine since Israel's inception has been a justified attempt at reclaiming the homeland for the displaced peoples.
• The Peloponnesian War was waged against the growing Athenian Empire by a collection of Greek city-states (including Athens) in order to thwart growing animosities and aggressions by the Athenians.

These models represent instances where the greatest good and utility was spread amongst the greatest amount of people, because war had been waged. War, like other forms of violence, should only come as a means of defending national sovereignty and/or deterring international aggression such as the Germans in World War II.

Act utilitarianism tells us that we must utilize war only in instances when other resources have been exhausted and there is no other clear choice that will serve the welfare of the entire populace. Often times, war ends up destroying large numbers of people on both sides; however, hindsight has told us that if certain aggressors were not stopped then they surely would have destroyed far more than the cumulative casualties and expenses of war.

Act utilitarianism does not justify wars fought for economic (imperialistic), cultural,