Prior to Chandragupta's consolidation of power, small regional kingdoms dominated the northwestern sub-continent, while the Nanda Empire dominated the Gangetic plain. After Chandragupta's conquests, the Maurya Empire extended from Bengal and Assam in the east, to Afghanistan and Balochistan in the west, to Kashmir and Nepal in the north, and to the Deccan Plateau in the south.
His achievements, which ranged from defeating Alexander's Macedonian satrapies and conquering the Nanda Empire by the time he was only about 20 years old, to defeating Seleucus Nicator and establishing centralized rule throughout Southern Asia, remain some of the most celebrated in Indian history. Over two thousand years later, the accomplishments of Chandragupta and his successors, including Asoka the Great, are objects of great study in the annals of South Asian and world history.
While many Indian historians hold the view that Chandragupta was an illegitimate child of the Nanda Dynasty of Magadha in eastern India, born to a Nanda prince and a maid named "Mura", other later literary traditions imply that Chandragupta may have been raised by peacock-tamers (Mayura-Poshaka), which earned him the Maurya epithet. Both the Buddhist as well as Jaina traditions testify to the supposed connection between the Moriya (Maurya) and Mora or Mayura (Peacock). Yet there are other literary traditions according to which Chandragupta belonged to Moriyas, a Kshatriya (warrior) clan of a little ancient republic of Pippalivana located between Rummindei in the Nepali Terai and Kasia in the Gorakhpur district of Uttar Pradesh.
There are differing theories regarding Chandragupta Maurya’s origins. Some regard Chandragupta to have originated from Magadha, possibly as the son of a Nanda prince and a maid named "Mura". A kshatriya people known as the "Mauryas" who had received the relics of the Buddha are also mentioned in the Mahaparinibbana Sutta of the Digha Nikaya. Then the Moriyas of Pipphalivana came to know that at Kusinara the Blessed One had passed away. And they sent a message to the Mallas of Kusinara, saying: "The Blessed One was of the warrior caste, and we are too. We are worthy to receive a portion of the relics of the Blessed One. We will erect a stupa over the relics of the Blessed One and hold a festival in their honor."
Others claim that the Mauryas were the Muras or rather Mors, and another view of a Jat origin of Indo-Scythian lineage has been proposed. Another school of thought, including scholars such as B. M. Barua, Dr J. W. McCrindle, Dr D. B. Spooner , Dr H. C. Seth , Dr Hari Ram Gupta , Dr Ranajit Pal and Kirpal Singh have connected Chandragupta to Gandhara (or Kamboja) in modern day Pakistan. Based on interpretations of Plutarch and Appian's writings, these scholars assert that Chandragupta Maurya may have belonged to the north-west frontier region, possibly to the Assakenoi or Ashvaka (q.v.) Kshatriya clan of Swat/Kunar valley (modern Koh-I-Mor or Mer-coh — the Meros of the classical writings; probably Meru of Sanskrit texts and Mor and Mer in Prakritic) . As Chandragupta belonged to this region (called Mor), the dynasty founded by him was called Moriya or Maurya . The Ashvakas were a section of the Kambojas, who were exclusively engaged in horse-culture and were noted for providing mercenary cavalry. .
See article: Saśigupta
Although no archaeological relics of Chandragupta Maurya are known from Patna or anywhere else, Dr. Ranajit Pal maintains that the two Laghman Aramaic inscriptions belong to Chandragupta Maurya, not Ashoka. H.C. Raychaudhuri noted that the name Priyadarshi was adopted also by Chandragupta and as noted by Sir W.W. Tarn, Vokhshu mentioned in these inscriptions was Oxyartes, a contemporary of Chandragupta, not Ashoka. Accoding to Pal, Orontobates who fought against Alexander the Great was Chandragupta. In many manuscripts of the Sanskrit drama Mudrarakshasa, Rantivarma takes the place of Chandragupta which shows that this was another name of Chandragupta like Sashigupta. Rantivarma is the same as Orontobates. Dr. Pal also suggests that Andragoras whose coins depict the famous Sun's quadriga was Androcottos or Chandragupta. From Diodorus' report it can be seen that Tiridates who handed over the fabulous treasury of Persepolis to Alexander, was in fact Chandragupta Dr. Pal also holds that Mithridates–II who, according to Diodorus, rose to the throne of Pontus in 337 B.C. (Diod. xvi. 90.) was Chandragupta.
Dr. Ranajit Pal makes the dramatic suggestion that Alexander the Great knew Orontobates intimately as there was a princess between the two. In his youth Alexander wanted to marry Ada II, the daughter of Pixodarus but this was negated by his father. Incidentally Orontobates married a daughter of Pixodarus, who was probably the same as Ada II. This makes it very likely that the relation between the two was far more complex than what Justin or even Plutarch knew.
Prof. Robin Lane Fox has written that Sisines the Persian who is said to have met Alexander in Cilicia was in fact an ally of the latter. Dr. Ranajit Pal suggests that Sisines was the same as Sisicottus or Sashigupta. He also makes the startling suggestion that Diodotus of Erythrae was the same as Chandragupta who had joined hands with the Generals to poison Alexander
According to traditional accounts, Chanakya, a teacher at Takshila University at the time of Alexander's invasion, found the boy Chandragupta from the Magadha kingdom in eastern India. As the story goes, Chandragupta was playing as a king with his friends and was giving justice to another boy playing criminal. Chanakya saw this and was impressed with Chandragupta's sense of justice. Chanakya asked his mother for him and then gave him education in Takshila.
"Androcottus, when he was a stripling, saw Alexander himself, and we are told that he often said in later times that Alexander narrowly missed making himself master of the country, since its king was hated and despised on account of his baseness and low birth."|20px|20px|Plutarch|Parallel Lives: Life of Alexander 62.9
According to this tradition, the encounter would have happened around 326 BCE, suggesting a birth date for Chandragupta around 340 BC.
Junianus Justinus (Justin) describes the humble origins of Chandragupta, and explains how he later led a popular uprising against the Nanda king:
"He was of humble origin, but was pushing to acquiring the throne by the superior power of the mind. When after having offended the king of Nanda by his insolence, he was condemned to death by the king, he was saved by the speed of his own feet... He gathered bandits and invited Indians to a change of rule."|20px|20px|Junianus Justinus|Historiarum Philippicarum libri XLIV, XV.4.15
At the time of Alexander's invasion, Chanakya was a teacher at Taxila University. The king of Taxila and Gandhara, Ambhi (also known as Taxiles), made a treaty with Alexander and did not fight against him. Chanakya saw the foreign invasion against the Indian culture and sought help from other kings to unite and fight Alexander. Porus (Parvateshwar), a king of Punjab, was the only local king who was able to challenge Alexander at the Battle of the Hydaspes River, but was defeated.
Chanakya then went to Magadha further east to seek the help of Dhana Nanda, who ruled a vast Nanda Empire which extended from Bihar and Bengal in the east to eastern Punjab in the west, but he denied any such help. After this incident, Chanakya began sowing the seeds of building an empire that could protect Indian territories from foreign invasion into his disciple Chandragupta.
Chandragupta's adviser or prime minister Chanakya, who is also known as Kautilya and was the author of the Arthashastra, is regarded as the architect of Chandragupta's early rise to power. Chandragupta Maurya, with the help of Chanakya, began laying the foundation of the Maurya Empire. In all forms of the Chanakya legend, he is thrown out of the Nanda court by the king, whereupon he swears revenge. While in Magadha, Chanakya by chance met Chandragupta in whom he spotted great military and executive abilities. Chanakya was impressed by the prince's personality and intelligence, and immediately took the young boy under his wing to fulfill his silent vow.
Depending upon the interpretation of Justin's accounts, the second version of the above story is that Chandragupta had also accompanied Chanakya to Pataliputra and himself was insulted by Dhana Nanda (Nandrum of Justin). If this version of Justin's accounts is accepted, then the view that Chanakya had purchased Chandragupta from Bihar, on his way back to Taxila, becomes irrelevant. The shrewd Chanakya had trained Chandragupta under his expert guidance and together they planned the conquest of the Nanda Empire.
According to Plutarch, at the time of Alexander's Battle of the Hydaspes River, the size of the Nanda Empire's army further east numbered 200,000 infantry, 80,000 cavalry, 8,000 chariots, and 6,000 war elephants, which was discouraging for Alexander's men and stayed their further progress into India:
But this last combat with Porus took off the edge of the Macedonians' courage, and stayed their further progress into India. For having found it hard enough to defeat an enemy who brought but twenty thousand foot and two thousand horse into the field, they thought they had reason to oppose Alexander's design of leading them on to pass the Ganges, too, which they were told was thirty-two furlongs broad and a fathom deep, and the banks on the further side covered with multitudes of enemies. For they were told the kings of the Gandaritans and Praesians expected them there with eighty thousand horse, two hundred thousand foot, eight thousand armed chariots, and six thousand fighting elephants. Nor was this a mere vain report, spread to discourage them." |20px|20px|Plutarch|Parallel Lives, Life of Alexander 62.1-4
In order to defeat the powerful Nanda army, Chandragupta needed to raise a formidable army of his own.
After Alexander's death in 323 BC, Chandragupta, turned his attention to Northwestern India (modern Pakistan), where he defeated the satrapies (described as "prefects" in classical Western sources) left in place by Alexander (according to Justin), and may have assassinated two of his governors, Nicanor and Philip. The satrapies he fought may have included Eudemus, ruler in western Punjab until his departure in 317 BC; and Peithon, son of Agenor, ruler of the Greek colonies along the Indus until his departure for Babylon in 316 BC. The Roman historian Justin described how Sandrocottus (Greek version of Chandragupta's name) conquered the northwest:
"India, after the death of Alexander, had assassinated his prefects, as if shaking the burden of servitude. The author of this liberation was Sandracottos, but he had transformed liberation in servitude after victory, since, after taking the throne, he himself oppressed the very people he has liberated from foreign domination." |20px|20px|Junianus Justinus|Historiarum Philippicarum libri XLIV, XV.4.12-13
"He was of humble origin, but was pushing to acquiring the throne by the superior power of the mind. When after having offensed the king of Nanda by his insolence, he was condemned to death by the king, he was saved by the speed of his own feet"|20px|20px|Junianus Justinus|Historiarum Philippicarum libri XLIV, XV.4.15
"Later, as he was preparing war against the prefects of Alexander, a huge wild elephant went to him and took him on his back as if tame, and he became a remarkable fighter and war leader. Having thus acquired royal power, Sandracottos possessed India at the time Seleucos was preparing future glory."|20px|20px|Junianus Justinus|Historiarum Philippicarum libri XLIV, XV.4.19
Having consolidated power in the northwest, Chandragupta pushed east towards the Nanda Empire.
Chanakya had trained Chandragupta under his guidance and together they planned the destruction of Dhana Nanda. The Mudrarakshasa of Visakhadutta as well as the Jaina work Parisishtaparvan talk of Chandragupta's alliance with the Himalayan king Parvatka, sometimes identified with Porus.
It is noted in the Chandraguptakatha that the protagonist and Chanakya were initially rebuffed by the Nanda forces. Regardless, in the ensuing war, Chandragupta faced off against Bhadrasala – commander of Dhana Nanda's armies. He was eventually able to defeat Bhadrasala and Dhana Nanda in a series of battles, ending with the siege of the capital city Kusumapura and the conquest of the Nanda Empire around 321 BC, thus founding the powerful Maurya Empire in Northern India by the time he was about 20 years old.
Seleucus I Nicator, a Macedonian satrap of Alexander, reconquered most of Alexander's former empire and put under his own authority eastern territories as far as Bactria and the Indus (Appian, History of Rome, The Syrian Wars 55), until in 305 BC he entered in a confrontation with Chandragupta:
"Always lying in wait for the neighboring nations, strong in arms and persuasive in council, he [Seleucus] acquired Mesopotamia, Armenia, 'Seleucid' Cappadocia, Persis, Parthia, Bactria, Arabia, Tapouria, Sogdia, Arachosia, Hyrcania, and other adjacent peoples that had been subdued by Alexander, as far as the river Indus, so that the boundaries of his empire were the most extensive in Asia after that of Alexander. The whole region from Phrygia to the Indus was subject to Seleucus."|20px|20px|Appian|History of Rome, The Syrian Wars 55
The exact details of engagement are not known. As noted by scholars such as R. C. Majumdar and D. D. Kosambi, Seleucus appears to have fared poorly, having ceded large territories west of the Indus to Chandragupta. Due to his defeat, Seleucus surrendered Arachosia, Gedrosia, Paropamisadae, and Aria.
Mainstream scholarship asserts that Chandragupta received vast territory west of the Indus, including the Hindu Kush, modern day Afghanistan, and the Balochistan province of Persia. Archaeologically, concrete indications of Mauryan rule, such as the inscriptions of the Edicts of Ashoka, are known as far as Kandhahar in southern Afghanistan.
In exchange for this territory, Seleucus obtained five hundred war elephants, a military asset which would play a decisive role at the Battle of Ipsus in 301 BC. A matrimonial alliance was also agreed upon (called Epigamia in ancient sources, meaning either the recognition of marriage between Indians and Greeks, or a dynastic alliance):
"He (Seleucus) crossed the Indus and waged war with Sandrocottus [Maurya], king of the Indians, who dwelt on the banks of that stream, until they came to an understanding with each other and contracted a marriage relationship." | Appian|History of Rome, The Syrian Wars 55
"After having made a treaty with him (Sandrakotos) and put in order the Orient situation, Seleucos went to war against Antigonus."|20px|20px|Junianus Justinus|Historiarum Philippicarum libri XLIV, XV.4.15
It is generally thought that an alliance may have been made, and that a Seleucid princess was bethrothed to the Maurya Dynasty. In addition to this treaty, Seleucus dispatched an ambassador, Megasthenes, to Chandragupta, and later Deimakos to his son Bindusara, at the Mauryan court at Pataliputra (modern Patna in Bihar state). Later Ptolemy II Philadelphus, the ruler of Ptolemaic Egypt and contemporary of Ashoka the Great, is also recorded by Pliny the Elder as having sent an ambassador named Dionysius to the Mauryan court.
Classical sources have also recorded that following their treaty, Chandragupta and Seleucus exchanged presents, such as when Chandragupta sent various aphrodisiacs to Seleucus:
"And Theophrastus says that some contrivances are of wondrous efficacy in such matters [as to make people more amorous]. And Phylarchus confirms him, by reference to some of the presents which Sandrakottus, the king of the Indians, sent to Seleucus; which were to act like charms in producing a wonderful degree of affection, while some, on the contrary, were to banish love."|20px|20px|Athenaeus of Naucratis|Deipnosophistae, I.32
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. Megasthenes later recorded the size of Chandragupta's acquired army as 400,000 soldiers, according to Strabo:
"Megasthenes was in the camp of Sandrocottus, which consisted of 400,000 men" |20px|20px|Strabo|Geographica, 15.1.53
On the other hand, Pliny, who also drew from Megasthenes' work, gives even larger numbers of 600,000 infantry, 30,000 cavalry, and 9,000 war elephants:
"But the Prasii surpass in power and glory every other people, not only in this quarter, but one may say in all India, their capital Palibothra, a very large and wealthy city, after which some call the people itself the Palibothri,--nay even the whole tract along the Ganges. Their king has in his pay a standing army of 600,000 foot-soldiers, 30,000 cavalry, and 9,000 elephants: whence may be formed some conjecture as to the vastness of his resources."|20px|20px|Pliny|Natural History VI, 22.4