One thing i will point out that most people do not realise :
There was no Nanda empire. Or Mauryan Empire. Or Shunga empire. These are all dynasties of the SAME empire: Magadh Empire.
Stop using western minimalistic take towards Indian history. They call their history the Roman Empire. The Holy Roman Empire. The Byzantine Empire. Not broken up by dynasties such as Julio-Claudian Empire, Nervan Empire, Ottonian Empire or Komnenos Empire.
The Magadh Empire has similar growth patterns as Roman empire : Its core territory & capital remain in Magadh ( just as Roman empire till the very end remained based in Latium) and just like Rome expanded to incorporate nearby lands- such as Sabian & Etruscan lands into Rome proper, so too did magadha- they expanded to incoporate Vajji, Anga & Vanga into their core Magadh territory.
The Magadh Empire lasts from roughly 550s BCE- from the time of Bimbisar, to 50s BCE, when the last Kanva emperor was overthrown and the Satavahanas ruled over Magadh.
It is the most important empire in Indian history and its recognition for its contribution and scale cannot be comprehended, if its broken up to its individual dynasties.