Though Chandragupta has humble origin he was a man of infinite courage. He knew well art of exploiting a situation to his advantage. The people of Magadha were very much dissatisfied with the rule of Dhanananda who were an oppressive king.
Chandragupta was aware of this and decided take advantage of the situation and overthrow the Nandas from Magadha. Chandragupta first tried to convince Alexander, who was then camping somewhere in north-western India, about the misrule of the nandas.
Chandragupta also offered his assistance to Alexander in order to overthrow the Nanda ruler. This offended Alexander who ordered him to be put under arrest. Chandragupta, however, ma good of his escape and reached the forest of the Vindhyas. Sometime later Chandragupta wrested the throne of Magadha from the Nandas with a very small army.
This was possible as because Chandragupta had with him the support and services of a very intelligent a powerful man named Chanakya. After Chandragupta had become the ruler of Magadha Chanakya was appointed his minister.