Nanda dynasty was ruling over North India at the time of Alexander's invasion. This dynasty originated from the region of Magadha in ancient India during the 4th century BCE and lasted between 345–321 BCE. At its greatest extent, the empire ruled by the Nanda Dynasty extended from Bengal in the east, to the Punjab region in the west and as far south as the Vindhya Range.
To create the first great empire of north India, the Nanda kings built a vast army, consisting of 200,000 infantry, 80,000 cavalry, 8,000 war chariots, and 6,000 war elephants. Because of this army power the Nandas never had the opportunity to see the army face of Alexander who invaded North-western India at the time of Dhana Nanda. Alexander was forced to confine his campaign to the plains of Punjab and Sindh, for his forces mutinied at the river Beas and refused to go any further upon encountering.