Seleucus I Nicator position held Seleucid ruler
Chandragupta and the Eastern Provinces
Seleucus soon turned his attention once again eastward. 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. When Alexander died, the Wars of the Diadochi ("Successors") split his empire apart; as his generals fought for control of Alexander's empire. In the eastern territories, Seleucus I Nicator took control of Alexander's conquests. According to the Roman historian Appian:[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. The whole region from Phrygia to the Indus was subject to Seleucus.
The Mauryans then annexed the areas around the Indus governed by the four Greek satraps: Nicanor, Phillip, Eudemus and Peithon. This established Mauryan control to the banks of the Indus. Chandragupta's victories convinced Seleucus that he needed to secure his eastern flank. Seeking to hold the Macedonian territories there, Seleucus thus came into conflict with the emerging and expanding Mauryan Empire over the Indus Valley.In the year 306 BC, Seleucus I Nicator went to India and apparently occupied territory as far as the Indus, and eventually waged war with the Maurya Emperor Chandragupta Maurya. Only a few sources mention his activities in India. Chandragupta (known in Greek sources as Sandrokottos), founder of the Mauryan empire, had conquered the Indus valley and several other parts of the easternmost regions of Alexander's empire. Seleucus began a campaign against Chandragupta and crossed the Indus. Most western historians note that it appears to have fared poorly as he did not achieve his goals, even though what exactly happened is unknown. The two leaders ultimately reached an agreement, and through a treaty sealed in 303 BC, Seleucus abandoned the territories he could never securely hold in exchange for stabilizing the East and obtaining elephants, with which he could turn his attention against his great western rival, Antigonus Monophthalmus. The 500 war elephants Seleucus obtained from Chandragupta were to play a key role in the forthcoming battles, particularly at Ipsus  against Antigonus and Demetrius. The Maurya king might have married the daughter of Seleucus. According to Strabo, the ceded territories bordered the Indus:
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