Complex sentence: Under Chandragupta, the Mauryan Empire conquered the trans-Indus region, which was under Macedonian nvasion led by Seleucus I, a Greek general from Alexander's army.
Split into simpler sentences: Under Chandragupta, the Mauryan Empire conquered the trans-Indus region, which was under Macedonian rule. Chandragupta then defeated the invasion led by Seleucus I, a Greek general from Alexander's army.