Army An army ( from Latin " arma " " arms , weapons " via Old French " armée " , " armed " ( feminine ) ) , is a fighting force that fights primarily on land . In the broadest sense , it is the land - based military branch , service branch or armed service of a nation or state . It may also include other branches of the military such as the air force via means of aviation corps . Within a national military force , the word army may also mean a field army . They differ from army reserves who are activated only during such times as war or natural disasters . In several countries , the army is officially called the Land Army to differentiate it from an air force called the Air Army , notably France . In such countries , the word " army " on its own retains its connotation of a land force in common usage . The current largest army in the world , by number of active troops , is the People ' s Liberation Army of China with 2 , 250 , 000 active troops and 800 , 000 reserve personnel followed by the Indian Army with 1 , 129 , 000 active troops and 2 , 142 , 900 reserve personnel . By convention , irregular military is understood in contrast to regular armies which grew slowly from personal bodyguards or elite militia . Regular in this case refers to standardized doctrines , uniforms , organizations , etc . Regular military can also refer to full - time status ( standing army ) , versus reserve or part - time personnel . Other distinctions may separate statutory forces ( established under laws such as the National Defence Act ) , from de facto " non - statutory " forces such as some guerrilla and revolutionary armies . Armies may also be expeditionary ( designed for overseas or international deployment ) or fencible ( designed for – or restricted to – homeland defence ) . History . China . China has existed as a continuous culture for thousands of years ; the states of China raised armies for at least 1000 years before the Spring and Autumn Annals , which date back to the time of Sparta . By the Warring States Period , the crossbow had been perfected enough to become a military secret , with bronze bolts which could pierce any armor . Thus any political power of a state rested on the armies and their organization . China underwent political consolidation of the states of Han ( 韓 ) , Wei ( 魏 ) , Chu ( 楚 ) , Yan ( 燕 ) , Zhao ( 趙 ) , and Qi ( 齊 ) , until by 221 BCE , Qin Shi Huang ( 秦始皇帝 ) , the first emperor of the Qin dynasty , attained absolute power . This first emperor of China could command the creation of a Terracotta Army to guard his tomb in the city of Xi ' an ( 西安 ) , as well as a realignment of the Great Wall of China to strengthen his empire against insurrection , invasion , and incursion . Sun Tzu ' s " The Art of War " remains one of China ' s Seven Military Classics , even though it is two thousand years old . Since no political figure could exist without an army , measures were taken to ensure only the most capable leaders could control the armies . Civil bureaucracies ( 士大夫 ) arose to control the productive power of the states , and their military power . Sparta . The Spartan Army was one of the earliest known professional armies . Boys were sent to a barracks at the age of seven to train for being a soldier . At the age of thirty they were released from the barracks and allowed to marry and have a family . After that , men devoted their lives to war until their retirement at the age of 60 . Unlike other civilizations , whose armies had to disband during the planting and harvest seasons , the Spartan serf s or " helot s , " did the manual labor . This allowed the Spartans to field a full - time army with a campaign season that lasted all year . The Spartan Army was largely composed of hoplite s , equipped with arms and armor nearly identical to each other . Each hoplite bore the Spartan emblem and a scarlet uniform . The main pieces of this armor were a round shield , a spear and a helmet . Ancient Rome . The Roman Army had its origins in the citizen army of the Republic , which was staffed by citizens serving mandatory duty for Rome . Reforms turned the army into a professional organization which was still largely filled by citizens , but these citizens served continuously for 25 years before being discharged . The Romans were also noted for making use of auxiliary troops , non - Romans who served with the legion s and filled roles that the traditional Roman military could not fill effectively , such as light skirmish troops and heavy cavalry . After their service in the army they were made citizens of Rome and then their children were citizens also . They were also given land and money to settle in Rome . In the Late Roman Empire , these auxiliary troops , along with foreign mercenaries , became the core of the Roman Army ; moreover , by the time of the Late Roman Empire tribes such as the Visigoths were paid to serve as mercenaries . Medieval Europe . In the earliest Middle Ages it was the obligation of every aristocrat to respond to the call to battle with his own equipment , archers , and infantry . This decentralized system was necessary due to the social order of the time , but could lead to motley forces with variable training , equipment and abilities . The more resources the noble had access to the better his troops would be . The knight s were drawn to battle by feudal and social obligation , and also by the prospect of profit and advancement . Those who performed well were likely to increase their landholdings and advance in the social hierarchy . The prospect of significant income from pillage , and ransoming prisoners was also important . For the mounted knight war could be a relatively low risk affair . As central governments grew in power , a return to the citizen armies of the classical period also began , as central levies of the peasantry began to be the central recruiting tool . England was one of the most centralized states in the Middle Ages , and the armies that fought in the Hundred Years ' War were , predominantly , composed of paid professionals . In theory , every Englishman had an obligation to serve for forty days . Forty days was not long enough for a campaign , especially one on the continent . Thus the scutage was introduced , whereby most Englishmen paid to escape their service and this money was used to create a permanent army . However , almost all high medieval armies in Europe were composed of a great deal of paid core troops , and there was a large mercenary market in Europe from at least the early 12th century . As the Middle Ages progressed in Italy , Italian cities began to rely mostly on mercenaries to do their fighting rather than the militias that had dominated the early and high medieval period in this region . These would be groups of career soldiers who would be paid a set rate . Mercenaries tended to be effective soldiers , especially in combination with standing forces , but in Italy they came to dominate the armies of the city states . This made them considerably less reliable than a standing army . Mercenary - on - mercenary warfare in Italy also led to relatively bloodless campaigns which relied as much on maneuver as on battles . Early modern . First nation - states lacked the funds needed to maintain standing forces , so they tended to hire mercenaries to serve in their armies during wartime . Such mercenaries typically formed at the ends of periods of conflict , when men - at - arms were no longer needed by their respective governments . The veteran soldiers thus looked for other forms of employment , often becoming mercenaries . Free Companies would often specialize in forms of combat that required longer periods of training that was not available in the form of a mobilized militia . As late as the 1650s , most troops were mercenaries . However , after the 17th century , most states invested in better disciplined and more politically reliable permanent troops . For a time mercenaries became important as trainers and administrators , but soon these tasks were also taken by the state . The massive size of these armies required a large supporting force of administrators . The newly centralized states were forced to set up vast organized bureaucracies to manage these armies , which some historians argue is the basis of the modern bureaucratic state . The combination of increased taxes and increased centralisation of government functions caused a series of revolts across Europe such as the Fronde in France and the English Civil War . In many countries , the resolution of this conflict was the rise of absolute monarchy . Only in England and the Netherlands did representative government evolve as an alternative . From the late 17th century , states learned how to finance wars through long term low interest loans from national banking institutions . The first state to master this process was the Dutch Republic . This transformation in the armies of Europe had great social impact . The defense of the state now rested on the commoners , not on the aristocrats . However , aristocrats continued to monopolise the officer corps of almost all early modern armies , including their high command . Moreover , popular revolts almost always failed unless they had the support and patronage of the noble or gentry classes . The new armies , because of their vast expense , were also dependent on taxation and the commercial classes who also began to demand a greater role in society . The great commercial powers of the Dutch and English matched much larger states in military might . As any man could be quickly trained in the use of a musket , it became far easier to form massive armies . The inaccuracy of the weapons necessitated large groups of massed soldiers . This led to a rapid swelling of the size of armies . For the first time huge masses of the population could enter combat , rather than just the highly skilled professionals . It has been argued that the drawing of men from across the nation into an organized corps helped breed national unity and patriotism , and during this period the modern notion of the nation state was born . However , this would only become apparent after the French Revolutionary Wars . At this time , the levée en masse and conscription would become the defining paradigm of modern warfare . Before then , however , most national armies were in fact composed of many nationalities . In Spain armies were recruited from all the Spanish European territories including Spain , Italy , Wallonia ( Walloon Guards ) and Germany . The French recruited some soldiers from Germany , Switzerland as well as from Piedmont . Britain recruited Hessian and Hanovrian troops until the late 18th century . Irish Catholics made careers for themselves in the armies of many Catholic European states . Prior to the English Civil War in England , the monarch maintained a personal Bodyguard of Yeomen of the Guard and the Honourable Corps of Gentlemen at Arms or ' gentlemen pensioners ' , and a few locally raised companies to garrison important places such as Berwick on Tweed or Portsmouth ( or Calais before it was recaptured by France in 1558 ) . Troops for foreign expeditions were raised upon an ad - hoc basis . Noblemen and professional regular soldier s were commissioned by the monarch to supply troops , raising their quotas by indenture from a variety of sources . On January 26 , 1661 Charles II issued the Royal Warrant that created the genesis of what would become the British Army , although the Scottish and English Armies would remain two separate organizations until the unification of England and Scotland in 1707 . The small force was represented by only a few regiments . After the American Revolutionary War the Continental Army was quickly disbanded as part of the Americans ' distrust of standing armies , and irregular state militias became the sole ground army of the United States , with the exception of one battery of artillery guarding West Point ' s arsenal . However , because of continuing conflict with Native Americans , it was soon realized that it was necessary to field a trained standing army . The first of these , the Legion of the United States , was established in 1791 . Until 1733 the common soldiers of Prussian Army consisted largely of peasantry recruited or impressed from Brandenburg - Prussia , leading many to flee to neighboring countries . To halt this trend , Frederick William I divided Prussia into regimental cantons . Every youth was required to serve as a soldier in these recruitment districts for three months each year ; this met agrarian needs and added extra troops to bolster the regular ranks . Russian tsar s before Peter I of Russia maintained professional hereditary musketeer corps ( streltsy in Russian ) that were highly unreliable and undisciplined . In times of war the armed forces were augmented by peasants . Peter I introduced a modern regular army built on German model , but with a new aspect : officers not necessarily from nobility , as talented commoners were given promotions that eventually included a noble title at the attainment of an officer ' s rank . Conscription of peasants and townspeople was based on quota system , per settlement . Initially it was based on the number of households , later it was based on the population numbers . The term of service in the 18th century was for life . In 1793 it was reduced to 25 years . In 1834 it was reduced to 20 years plus 5 years in reserve and in 1855 to 12 years plus 3 years of reserve . The first Ottoman standing army were Janissaries . They replaced forces that mostly comprised tribal warriors ( " ghazi s " ) whose loyalty and morale could not always be trusted . The first Janissary units were formed from prisoners of war and slaves , probably as a result of the sultan taking his traditional one - fifth share of his army ' s booty in kind rather than cash . From the 1380s onwards , their ranks were filled under the " devşirme " system , where feudal dues were paid by service to the sultan . The " recruits " were mostly Christian youths , reminiscent of Mamelukes . China organized the Manchu people into the Eight Banner system in the early 17th century . Defected Ming armies formed the Green Standard Army . These troops enlisted voluntarily and for long terms of service . Late modern . Conscription allowed the French Republic to form the " La Grande Armée " , what Napoleon Bonaparte called " the nation in arms " , which successfully battled European professional armies . Conscription , particularly when the conscripts are being sent to foreign wars that do not directly affect the security of the nation , has historically been highly politically contentious in democracies . Canada also had a political dispute over conscription during World War II . Similarly , mass protests against conscription to fight the Vietnam War occurred in several countries in the late 1960s . In developed nations , the increasing emphasis on technological firepower and better - trained fighting forces , the sheer unlikelihood of a conventional military assault on most developed nations , as well as memories of the contentiousness of the Vietnam War experience , make mass conscription unlikely in the foreseeable future . Russia , as well as many other nations , retains mainly a conscript army . There is also a very rare " citizen army " as used in Switzerland ( see Swiss army ) . Armies as armed services . Western armies are usually subdivided as follows : Field army . A field army is composed of a headquarters , army troops , a variable number of corps , typically between three to four , and a variable number of divisions , also between three to four . A battle is influenced at the Field Army level by transferring divisions and reinforcements from one corps to another to increase the pressure on the enemy at a critical point . Field armies are controlled by a General or Lieutenant General . Formations . A particular army can be named or numbered to distinguish it from military land forces in general . For example , the First United States Army and the Army of Northern Virginia . In the British Army it is normal to spell out the ordinal number of an army ( e . g . First Army ) , whereas lower formations use figures ( e . g . 1st Division ) . Armies ( as well as army group s and theater s ) are large formations which vary significantly between armed forces in size , composition , and scope of responsibility . In the Soviet Red Army and the Soviet Air Force , " Armies " could vary in size , but were subordinate to an Army Group - sized " front " in wartime . In peacetime , a Soviet army was usually subordinate to a military district . Viktor Suvorov ' s " Inside the Soviet Army " describes how Cold War era Soviet military districts were actually composed of a front headquarters and a military district headquarters co - located for administration and deception ( ' maskirovika ' ) reasons .