The military history of India dates back to almost the 6th century BC. It encompassed the period when some of the more aggressive forces like the Persians, Greeks, the Turks, Huns, Mongols and so on crossed over into the more fertile and alluvial plains of India from the north-western route.
Very little details with regard to the early conflicts between the invading forces are available. However, as per the evidence, some of the invaders did manage to slowly overrun western India and consolidated their hold along the Indo - Gangetic plains. In this process, they subdued numerous native tribal kingdoms through pitched battles.
They advanced further south till the time they generally halted by the jungle which covered Vindhya Mountains. Apart from this, there were also certain other areas along the western coast and the Deccan plateau which were hilly and sparse. As a result, these places were unsuitable for the movements of considerable bodies of people.
However, this vast area also provided some sort of a favorable resistance against invasion by loose fighting warriors. Like for instance, the Marathas who subsequently became a force to reckon with. The other major pre-condition of war in India was and continued to be the climate. Monsoon rains between June and September rendered movement of armies virtually impossible.
The best season for campaigning was always October and November. During this time, the crops were ripe, the herbage green and it was possible to live away from the country for a while then. Between foreign invasions, wars in the north also emerged as a favorite sport of kings and noblemen. These wars rarely became a national struggle for existence except when a new invader from the northwest entered the conflict.
The armies of the native tribes consisted mostly of foot-soldiers. These subsequently came to be known as the infantry. The bow and arrow were their chief weapons. Cavalry was not in existence as horses were scare. Around 537 BC Cyrus of Persia reached the region of modern Peshawar. His successor Darius conquered part of north-western Punjab.
Their invasions brought home to the Indians the importance and utility of cavalry, however Indian climate conditions were not conducive for the breeding of good horses, and therefore reserved for pulling the war chariots of kings and nobles. So the infantry continued to be relied upon as the crucial weapon of war. Warriors were the most honored and leading classes of society.
Wars were usually fought with restricted objectives. They were fought for the most part with far less savagery than elsewhere in the world. It was very rare that the locals indulged in mass slaughter after a victory. Such chivalrous and rather ritualistic conduct of war made conquest by less scrupulous invaders rather easy.
The first definite recorded fact in Indian political history was the invasion by the Greeks under the leadership of Alexander the Great. This invasion took place during 327-26 BC. After crossing the Hindu Kush Mountains, Alexander captured the city of Taxila and defeated India's King Porus at the battle of the Jhelum. Jhelum was also referred to as Hydespes by the Greeks.