Maurya dynasty overthrown by the Shunga dynasty during 185 BCE. Pushyamitra Shunga was the founder of the dynasty. He was commander-in-chief(senapati) of the last Maurya King Brihadratha. While king was reviewing the Guard of Honor of his forces, Pushyamitra assassinated him and ascended throne.
Because of the weaker rulers after Ashoka, Magadha empire started to shrink. By the time when Pushyamitra sized throne, Magadha left only fraction of its original size. It reduced only to three states Pataliputra, Ayodhya, Vidisha and some parts of Punjab. Shunga dynasty known to have fought war with Kalingas, Satvahans, the Indo-greeks and possibly Panchals and Mathura.