Answer:
The Ganges Basin
Step-by-step explanation:
Before Chandragupta took control of this territory, the Ganges Basin was controlled by Nanda Empire. This empire was led by a king named Dhana Nanda. The Basin connected Indian territory with the middle east, so conquering this territory will be beneficial for the Maurya empire in terms of trades.
The War for the conquest for this region occurred in 321 BC. Chandragupta managed to won the war after continually pressure Nanda Empire for around 1 year.