The Gupta empire ruled between A.D 300 to A.D 550. Between the Mauryan dynasty and the Gupta period, the large empire was broken into smaller Kingdoms under Kanishka, Satvahanas and the Kalinga rulers. The basic organization of the army and its employment in battle remained similar over the years.
The military of the Gupta Empire remained based on the traditional four part armies or Chaturangabala. They, unlike other armies, included a mounted cavalry by this time. They modeled the dress and armor of their cavalry after the well-crafted and equipped soldiers of the Kushan empire.
The Guptas preferred armored cavalry forces that attacked with lances or swords. The weapons used such as bow and arrow were made of metal instead of bamboo or wood as in earlier times. The Guptas seem to have relied heavily on infantry archers, and the bow was the dominant weapon of their army. The version of the longbow was composed of metal, or more typically bamboo, and fired a long bamboo cane arrow with a metal head. The longbow was reputedly a powerful weapon capable of great range and penetration and provided an effective counter to invading horse archers. Iron shafts were used against armored elephants. Fire arrows were not part of the bowmen's arsenal contrary to popular belief.
The era of the Gupta Empire in India was all about conquering. The rulers wanted to expand their reach across India. They did this by attacking the Kingdoms around them to gain land. Samudragupta, son of Chandragupta, was a King out for conquest. He desired to unite all of India under his rule and quickly set out to accomplish this dream by starting wars across much of the Indian region.
During the reign of Chandragupta II, Gupta Empire maintained a large army consisting of 500,000 infantry, 50,000 cavalry, 20,000 charioteers and 10,000 elephants along with a powerful navy with more than 1200 ships. Chandragupta II controlled the whole of the Indian subcontinent; the Gupta Empire was the most powerful empire in the world during his reign. The reason for conquest and building a large empire was to protect the Kingdom from disintegrating into smaller ones thus dissipating power.
The decline of Mauryan and Gupta period led to such a disintegration and weakening of the forces thus the invaders such as the Sultanates were able to overcome the later Kings and establish their control over India.