Infantry (Infantrymen) are soldiers who fight primarily on foot, using personal weapons. They may arrive on scene in various ways, and are deployed either in formations or as skirmishers and guerillas. In the modern period, the term infantrymen is reserved for the most basic of infantry troops, the rifleman.
Infantry have been the core of most armies throughout history. In ancient times the most prominent formations were the phalanx and later the more sophisticated legion, which could reach several thousand men in size. After the Roman Empire collapsed cavalry dominated the west for almost a thousand years; particularly later in the Middle Ages when the armoured knight was invincible. The dominance of cavalry was not threatened until the Hundred Years War, where the development of the longbow saw French knights heavily defeated by well-disciplined infantry, archers, and dismounted cavalry at the battles of Crecy, Poitiers and Agincourt. From this time on, cavalry became lighter and more mobile, and infantry became, in general, the most important arm.
Although the longbow would remain significantly more powerful than the newly invented musket for some hundreds of years - longbows had greater range, accuracy, penetrating power and rate of fire than early firearms - it required great skill to use effectively. It took a lifetime of training to become an effective archer, where to raise an army of musketeers simply needed ample numbers of men who could be trained in weeks or months, enough money, and access to manufacturing facilities for guns and powder. From the late Middle Ages on, industrialisation saw rural aristocracies weaken, cities became richer, and large, easily raised forces of relatively untrained infantry ruled the battlefield. With cavalry now lighter and unarmoured, the pike became an important close-range defence for bodies of well-drilled infantry.
Before the development of railroads in the 19th century, infantry armies got to the battlefield by walking, or sometimes by ship. In the 1890s and later, some countries used bicycle infantry, but the real revolution in mobility started in the 1920s with the use of motor vehicles, resulting in motorised infantry. Action in World War II demonstrated the importance of protecting the soldiers while they are moving around, resulting in the development of mechanized infantry that uses armoured vehicles for transport.
Modern-day infantry is supported by armoured fighting vehicles, artillery, and aircraft, but are still the only kind of military force that can take and hold ground, and thus remain essential to fighting wars.
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See also: army, marine, military history, military science, Zouave