War

War is a prolonged state of violent conflict between two states. War has been conducted for many purposes, such as the acquisition of goods, seizing enemy territory, to satisfy the honor of the sovereign, eliminating a threat to the homeland, stamping out rival religious sects (see Religious_war), or exporting political ideologies. Warfare between factions within a single state is called civil war.

Wars have often been periods of great technological innovation as each side finds itself faced with the necessity of creating new methods of offense and defense to ensure national survival. The American Civil War, coming only a decade after the Industrial revolution took root in the United States, introduced mechanized warfare to the world with metal warships, railroad transportation of forces and material, and instant communication via the telegraph. The conflict known as the Great War (later called World War I) introduced air combat, chemical warfare, submarine and tank warfare, and the large scale deployment of the machine gun. World War II refined tank tactics in the form of the Blitzkrieg as the aircraft carrier took mastery of the seas. It ended with the first use of nuclear weapons in wartime.

The decades after World War II saw America emerge as a military colossus, unchallenged and irresistable on the battlefield head-on, but vulnerable to a new type of asymmetrical warfare against an enemy who shuns uniforms, hides among the populace, and employs cheap but effective improvised weapons against multi-million dollar U.S. hardware.