War, a contest between nations and States (international war), or between parties in the same State (civil war), carried on by force of arms, and resorted to either for purposes of advantage or of revenge. Formerly, war was waged at the will of despotic monarchs; now wars usually arise, in the first instance, from disputes concerning territorial possessions and frontiers, unjust dealings with the citizens of one State by another, questions of race and sentiment, jealousy of military prestige, or mere lust of conquest. Civil wars arise from the claims of rival competitors for the supreme power in a State, or for the establishment of some important point connected with civil or religious liberty. In all cases, the object of each contending party is to destroy the power of the other by defeating or dispersing his army or navy, by the occupation of some important part of his country, such as the capital, or the principal administrative and commercial centers, or the ruin of his commerce, thus cutting off his sources of recuperation in men, money, and material. An international or public war can only be authorized by the sovereign power of the nations, and previous to the commencement of hostilities it is now usual for the State taking the initiative to issue a declaration of war, which usually takes the form of an explanatory manifesto addressed to the neutral States. An aggressive or offensive war is one carried into the territory of a hitherto friendly power; and a defensive war is one carried on to resist such aggression. Certain laws, usages, or rights of war are recognized by international law. By such laws it is allowable to seize and destroy the persons or property of armed enemies, to stop up all their channels of traffic or supply, and to appropriate everything in an enemy's country necessary for the support of subsistence of the invading army. On the other hand, though an enemy may lawfully be starved into a surrender, wounding, except in battle, mutilation, and all cruel and wanton devastation, are contrary to the usages of war, as are also the bombarding of a defenseless town, firing on a hospital, the use of poison in any way, or torture to extort information from an enemy.
Entry from Everybody's Cyclopedia, 1912.