The Mauryan empire was first expanded by King Chandragupta, the first ruler of the Mauryans.  He conquered the Magadha people in a campaign to increase his territory.  Following Chandragupta's rule, the Mauryan territory remained more or less fixed.  King Ashoka did wage war during the beginning of his reign, conquering the Kalinga people, his southern neighbor.  According to one of the stone edicts, when Ashoka conquer Kalinga, he took 150,000 prisoners, killed another 100,000, and injured countless others.  Ashoka was horrified by the death and destruction he had caused.  Ergo, he converted to Buddhism and embraced pacifism, bringing about a cessation to the expansion of the Mauryan empire.  The Magadha and Kalinga people remained part of the Mauryan civilization, as did their respective territories.
        Chandragupta Maurya made a much greater contribution to the Mauryan empire than Ashoka did as far as land is concerned.  Chandragupta's conquered territories are shown in the map below, highlighted in yellow: