According to Buddhist, Jain, and Puranic traditions, the Nanda dynasty ruled over Magadha before Chandragupta overthrew it with the help of Chanakya.  The Chandragupta and Chanakya armies initially seized the Nanda outlying regions before besieging Pataliputra, the Nanda capital. Finally Dhana Nanda accepted defeat, bringing an end to the Nanda Empire (present Eastern India). The Puranic and Jain writings claim that the conflict was fiercely contested because the Nanda dynasty possessed a potent and well-trained army, in contrast to the Buddhist sources that portray the victory as being straightforward. 

Chandragupta then proceeded north–west to take advantage of the enormous power vacuum created by Alexander’s death in 323 BCE and thereby establishing the Mauryan Empire. These lands fell quickly to him till he reached the Indus. In order to gain control of satrapies in the Indus Valley and northwest India, Chandragupta undertook a number of military campaigns in 305 BCE.

Following the death of Alexander, Alexander’s successor, Seleucus Nicator, had reinforced his grasp on the territory. Chandragupta defeated Seleucus in 305 B.C., and eastern Afghanistan, Baluchistan, and Makran were surrendered to the Maurya. As a result, control of the routes and nodes in the northwestern region switched from Persian-Hellenistic to Mauryan. Seleucus received 500 elephants in exchange for the region he surrendered. There was also a Marriage agreement. The Mauryan Empire’s territorial base had been formed, with Chandragupta dominating the Indus and Ganges Plains along with the borders. Chandragupta expanded his realm after declaring himself king by using force and creating allies.

The defeat of the Seleucids resulted in the extension of the Mauryan Empire including the Gandhara civilization which has produced outstanding revenue since its incorporation into the Achaemenid Empire. It was also connected to the land routes leading to West Asia. The conquest of central India provided access to the peninsula, another territory with resources that northern powers had yet to harness.

Since the Peace treaty 303 BCE, The Mauryas and Seleucids enjoyed cordial relations. As a result, number of Greeks, including the historian Megasthenes, Deimakos, and Dionysius, lived at the Mauryan court and established the diplomatic ties. Most famous among the Greek ambassadors, was Megasthenes. His work ‘Indika’ describing the Mauryan society as freedom loving, gave the world in-depth knowledge about the Mauryan empire

According to Jaina traditions, Chandragupta, relinquished his throne in favor of his son Bindusara and became a monk. He traveled to south India with Bhadrabahu and other monks to end his life through regulated slow fasting in the traditional Jain way.