[b] The alliance freed Seleucus to turn his attention toward his rivals in the west, while Chandragupta secured control over the areas that he had sought, the Maurya Empire emerging as the dominant power of the Indian subcontinent.

In the wake of Alexander's Indian campaign, Chandragupta Maurya lead a successful revolt from north-western India against the Nanda Dynasty, rulers at the time of the Gangetic Plain, establishing himself as Emperor of Magadha around 321 BC.

The Persian provinces in what is now modern Afghanistan, together with the wealthy kingdom of Gandhara and the states of the Indus Valley, had all submitted to Alexander the Great and become part of his empire.

According to the Roman historian Appian, History of Rome, Seleucus was Always lying in wait for the neighboring nations, strong in arms and persuasive in council, he 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.

[8] According to Appian, [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.

According to Grainger, the details of the conflict are unclear, but the outcome clearly must have been "a decisive Indian victory," with Chandragupta driving back Seleucus' forces as far as the Hindu Kush and consequently gaining large territories in modern-day Afghanistan.

Alexander [III 'the Great' of Macedon] took these away from the Arians and established settlements of his own, but Seleucus Nicator gave them to Sandrocottus [Chandragupta], upon terms of intermarriage and of receiving in exchange five hundred elephants.

by Seleukos Nikator to Chandragupta Maurya included provinces of the Paropanisadae (Kabul), Aria (Herat), Arachosia (Kandahar), and probably Gedrosia (Makran), or a large part of that satrapy.

(iii) The two kings were joined by some kind of marriage alliance (ἐπιγαμία οι κῆδος); most likely Chandragupta wed a female relative of Seleucus.

The Malin range of mountains,[d] which Alexander experienced such difficulty in crossing,[e] would have furnished a natural boundary.Tarn limits the ceded part of Gedrosia to the territory east of the Porali Hingol) river, referring to Eratosthenes (c.276 BC – c.195/194 BCE), who states (in Tarn words) that Alexander [...] took away from Iran the parts of these three satrapies which lay along the Indus and made of them separate [...] governments or province; it was these which Seleucus ceded, being districts predominantly Indian in blood.

"[25]In History of Early India, also from 1963, Thapar writes that "Some Seleucid territories that today would cover eastern Afghanistan, Baluchistan and Makran were ceded to the Maurya.

"[16] Thomas Trautmann includes the Makran Coast, referring to Smith (1924), and taking the Ashokan Edict of Kandahar as a validation for a maximum interpretation of Strabo.

[32]According to Tarn, explicitly criticising Smith for his interpretation of the extent of Aria,[l] the idea that Seleucus handed over more than what is now eastern Afghanistan is an exaggeration originating in a statement by Pliny the Elder in his Geographia VI, 69, referring not specifically to the lands received by Chandragupta, but rather to the various opinions of geographers regarding the definition of the word "India.

[9] The border between the Seleucid and Mauryan Empires remained stable in subsequent generations, and friendly diplomatic relations are reflected by the ambassador Megasthenes, and by the envoys sent westward by Chandragupta's grandson Ashoka.

Chandragupta's gift of war elephants "may have alleviated the burden of fodder and the return march"[9] and allowed him to appropriately reduce the size and cost of his large army, since the major threats to his power had now all been removed.

Adding Antigonus's territories to his own, Seleucus would found the Seleucid Empire, which would endure as a great power in the Mediterranean and the Middle East until 64 BC.