Engaging in armed struggle, whether between nations, races, cultures or other groupings, using various sized units in the air, at sea or on land. Combat between troops (as opposed to destruction of objects) is usually used to capture or retain important areas of territory (usually where rival claims for essential resources are involved); but it is also used to change or maintain political systems or leadership, to subject or free a people, or to prevent full-scale war.
Throughout the history of war the forms and methods of interpersonal combat have been altered, due to the development of weapons, organization of troops and the skill of military leadership. There is no way of determining the beginning of combat but the philosophy of war begins with "The Art of War" by Sun Tzu in the period of 400-320 BC. "To win one hundred victories in one hundred battles is not the acme of skill. To subdue the enemy without fighting is the acme of skill". The application of gunpowder to weapons in 14th century Europe changed the form of warfare from what was essentially groups of individuals in combat in a limited area using arrows, spears, lances and staves, to groups of units using smooth bore cannon and shotguns. The development of rifles in the 19th century increased the range, accuracy and speed of fire, causing extended formation tactics. With the invention of the aeroplane at the turn of the century and rockets during World War II, the effective range of battle was extended to the continental and intercontinental levels with the concomitant introduction of absolute war involving destruction of non-military targets and populations.
Combat between troops is an effective way to test the resolve of nations in conflict and the only way to defend against aggression and abuses of human rights, under which conditions warfare is justified. Defensive war is also always justified.
War inevitably leads to further war. It is barbaric and a criminal waste of human life. There is no justification for it.