Magadha was controlled by the Nanda Dynasty, that had an extremely well equipped, strong and resourceful army. In order to conquer it, Chandragupta built an alliance with Chanakya that was powerful enough to begin war. Although they had an extremely hard time against them at first, the new alliance eventually defeated Nanda's forces after several battles. The defining factor ended up being the Siege on the capital city of Pataliputra, which guaranteed Candragupta's success taking over Magadha.
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