An army, 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, versus reserve or part-time personnel. Other distinctions may separate statutory forces, from de facto "non-statutory" forces such as some guerrilla and revolutionary armies. Armies may also be expeditionary or fencible .
India has had some of the earliest armies in the world. During the Indus Valley Civilization however, There was just a short guard force as they didn't fear invasion at the time. After the Aryan invasion, kingdoms and city-states started forming with armies to protect the city. One of the first known recorded battles, happened when a Hindu king defeated an alliance of ten kings. During the Iron Age, The and had large armies the peak being 639,100 soldiers. In the age large armies of Longbowmen were recruited to...