At that time, Magadh was ruled by the Nanda dynasty whose rule was unpopular. Chandragupta founded the Mauryan Empire by overthrowing the Nanda dynasty with the help of Chanakya (also Kautilya) who was an important minister in the court of the Nanda rulers. Chanakya was ill treated by the Nanda king and he vowed to destroy their kingdom. He met the young Chandragupta in the Vindhya forest. As Chanakya was well versed in politics and the affairs of the state, he groomed Chandragupta and helped him raise and organize an army. Thus, with the help of Chanakya, Chandragupta overthrew the last Nanda ruler and became the king. Chanakya became the chief minister in the court of Chandragupta.
The invasion of the northwestern part of India by Alexander in 326 BC and the subsequent establishment of the rule of Seleucus Nikator (one of Alexander's general) was a thorn in the eyes of Chandragupta. Chandragupta firstly stabilized his power in Magadh and then began his campaign against Seleucus.
After a prolonged struggle, Chandragupta was able to defeat Seleucus in 305 BC and annexed the entire Punjab and areas across the Indus River. According to the peace treaty with Seleucus, Chandragupta also got Kabul, Gandhara, and parts of Persia and married his daughter. In this way, Chandragupta became the undisputed ruler of Northern India.
After annexing Seleucus' eastern Persian provinces, Chandragupta had a vast empire extending across the northern parts of Southern Asia, from the Bay of Bengal to the Arabian Sea. Chandragupta then began expanding his empire further south beyond the barrier of the Vindhya Range and into the Deccan Plateau. By the time his conquests were complete, Chandragupta succeeded in unifying most of Southern Asia. As a result, Chandragupta is considered the first unifier of India and the first genuine emperor of India.
His fame was so widespread that rulers from far off kingdoms send their envoys to his court. Chandragupta also conquered parts of Central India and united the whole of northern India under Mauryan rule. After ruling for about 25 years, he became a Jain ascetic and left his throne to his son Bindusara (296 BC-273 BC).