Chandragupta Maurya once saw 16 dreams & went to Digambar Jain naked monk Bhadrabahuji, who was the last Shrut-kevali of this time cycle according to jainism. Bhadrabahuji, being shrut keveli & avadhi gyani can predict future. When Chandragupta Maurya described his 16 dreams, he told him the meaning of this 16 dreams & predicted that according to these dreams, there was going to be long & severe famine in the kingdom of Magadha (in modern Bihar) i.e. central India & forthcoming time wasn't good for Jain monks & it will also affect badly the followers of Jain religion.
Great Jain saint & last Shrut-kevali Acharya Bhadrabahuji was the head of the entire jain sangh (i.e. a group of jain monks) that time. There were around group of 24000 Jain monks. With a view to avoid the terrible effects of famine Shri Bhadrabahu, along with a body of 24,000 jain monks, decided to migrate from Pataliputra, the capital of Magadha, to Shravanabelagola (in modern Karnataka State) in South India for the time of famine, so that they do not get affected by the effects of famine & could keep up the muni-dharma. But out of 24000 monks, around 12000 opposed this decision & refused to come with Acharya Bhadrabahu, while remaining 12000 supported his decision & decided to join their head Acharya Bhadrabahu & come with him to south. Hence, Bhadrabahu migrated to Shravanabelagola with group of 12000 jain monks & remaining 12000 jain monks stayed who refused to migrate stayed back in Magadha under the leadership of monk Sthulibhadra
After hearing the meaning of his dreams, Chandragupta decided to take Jina-deeksha (i.e. become a jain saint) from Bhadrabahuji & became jain-monk. Chandragupta was Emperor of Magadha & devoted to Ächärya Bhadrabahu, abdicated his throne in favor of his son Bindusara, joined Bhadrabahu’s entourage as a monk‑disciple & stayed with Bhadrabahu at Shravanabelagola for 12 years after death of his teacher Bhadrabahu, in about 297 B.C. died after practicing penance according to the strict Jain rite of Sallekhana on same hill at Shravanabelagola. This Bhadrabahu Chandragupta tradition is strongly supported by large number of epigraphic & literary evidences of very reliable nature.
To know more about relation between Shri Bhadrabahu-1, Chandragupta Maurya & Chanakya. refer http://groups.yahoo.com/group/JatHistory/message/5098
So, we see that till Bhadrabahu the entire Jain sangh (jain sangh means group of jain monks) was one & united. i.e. there was no sect or sub-sect amongst jainism, everyone were Digambaras & there was no other sects or sub-sects of jainism like shwetambaras or sthankvashis sect & there was only Digambar tradition in that time...
Now, let us have pre-cap to our initial topic to understand division of jain religion into sectos:- As wrote above, Chandraguta became jain monk & joined the sangha of 12000 monks led by Bhadrabahuji. The sangha went to south India. At Sravanbelgola region of Karnataka, Bhadrabahu felt that now his life is going to end, so he asked the sangh to leave him there & go to Chola-desh (Tamil Nadu). But, monk Chandragupta remained with Bhadrabahuji to serve him.
The remaining sangh under the leadership of Vishaknandiji went to south. When the Jain sangh lead by Vishakhnandiji came to Chandraguptaji, they thaught that he that he has got corrupt as it was not possible for jain monk to follow jain muni-dharma conduct as per Jin-Vaani (means preachings of Lord). But, when Chandragupta asked the sangh to have Ahaar (Ahaar means food taken by jain monk from pure jain shravakas i.e. devotee as per strict rules for monk) in the town, they really found a town & a lot of shravakas (shravakas means jain devotees) there.They appologised to Chandraguptaji & went Northwards.
When the ascetics of Bhadrabahu‑sangha returned to Pataliputra of Kingdowm Magadha after the end of 12 year period of famine, they, to their utter surprise, noticed 2 significant changes that had taken place during their absence. Among the 12000 ascetics of Magadha under the leadership of Ächärya Sthulibhadra, In the first place, the rule of nudity was relaxed & the ascetics were allowed to wear a piece of white cloth (known as Ardhaphalaka). Secondly, the sacred books were collected & edited (adultrated) at the council of Pataliputra in their absense in which they found some inconsistencies. As a result the group of returned monks did not accept the two things, introduced by the followers of Ächärya Sthulibhadra, namely, the relaxation of the rule of nudity & the recension of the sacred texts, & proclaimed themselves as true Jains. Eventually, Jain religion was split up into two distinct sects, viz., Digambara (stark naked) and Shvetämbar (white-clad) about 600 years after Nirvän of Lord Mahavir.