Treta Yuga 2
1000 BC to 250 BC
Mbh.12.336:- After the expiration of this the Krita age, when the Treta age comes in course of the Vivaswat cycle, a great calamity will overtake the worlds - a statement mentioned at the end of Krita-2 (1000 BC).
Bhikshus with Sectarian Marks
1000 BC onwards
Mbh.12.64:- After the expiry of this the Krita age, a confusion will set in, regarding the different modes of life, and innumerable Bhikshus will appear with sectarian marks of different kinds. Disregarding the Puranas and the high truths of religion, men, urged by lust and wrath, will deviate into Wrong paths.
The mention of Bhikshus (people who live by alms) with sectarian marks is a reference to Saiva and [wkipedia:Vaisnava] cults along with the cults of worship of Ganapati, Subrahmanya (Skanda / Kumara / Kartikeya / Muruka) and Devi (Kali / Mahadavi). Vaishnavas put a V shaped mark on their forehead while Saivas keep three parallel lines on their forehead. During this period not only the Vedas, even the Puranas that contains glimpses of Vedic thoughts are disregarded. People engaged in sectarian fights and were lustful and wrathful. They deviated into all kinds of wrong paths.
Animal Sacrifices, Life of Mahavira, Buddha
1000 BC onwards
As mentioned earlier, animal sacrifices that were prohibited during the Krita-2 (2000 BC to 1000 BC) period became acceptable during the Treta-2 period (1000 BC to 250 BC). The name of all kinds of sacrifices that were peaceful and symbolic became violent with slaying of animals. Gomedha started to mean slaying of cows, Aswamedha meant slaying of horses. Naramedha meant slaying of human beings! Aja which formerly meant vegetable seed started to mean goat and people slew goats for all kinds of sacrifices.
Probably due to this total violence and the promulgation of caste system (with 16 or 256 castes) in the society some section of the society reacted strongly to this corruption and lead to the emergence of Buddhism and Jainism. The philosophical thoughts behind these religion existed even during the time of Mahabharata. But these philosophies emerged into religion in this period. Mahavira was born in 599 BC in a place named Vaishali in Magadha kingdom. He founded the religion named Jainism and preached non-violence. Buddha was born in 563 BC as sage Sakya (a sage among the Sakas who ruled the Malla kingdom that then lied to the north of Kosala kingdom) in a city named Kapilavastu). He founded Buddhism and preached non violence. Both Mahavira and Buddha were the result of the reaction of the society towards the growing violence and caste intolerances.
Treta-2 Dwapara-2 Junction
350 BC to 250 BC
Mbh.12.206:- Those men, born in the southern region and are called Andrakas, Guhas, Pulindas, Savaras, Chuchukas, Madrakas Those that are born in the northern region, I shall also mention. They are Yamas, Kamvojas, Gandharas, Kiratas and Barbaras. All of them are sinful, and move on this Earth, characterised by practices similar to those of Chandalas and ravens and vultures. In the Krita age, they were nowhere on earth. It is from the Treta that they have had their origin and began to multiply. When the terrible period came, joining Treta and the Dwapara, the Kshatriyas, approaching one another, engaged themselves in battle.
Here we get a clear picture where the invading tribes mentioned in former Yugas (Kali-1 and Krita-2) went and settled. As per this the Andhras settled in the south along with the Guhas, Pulindas, Savaras and Madrakas. Many Madraka (Valhika / Bahlika) cultural traits like inheritance through sister's son is prevailed in south. The Yamas (probably referring to Yavanas), Kamvojas, Gandharas, Kiratas and Barbaras settled in the north. Though they started their invasion and assimilation starting from Kali-1 (3000 Bc to 2000 BC), in Krita-2 age (2000 BC to 1000 BC) their influence was feeble due to the role played by Kalki (1900 BC) who drove them off or subdued them. But in Treta-2 (1000 B to 250 BC), the influence of Kalki vanished and these tribes once again gained prominence. The junction of Treta-2 and Dwapara-2 is mentioned as witnessing terrible battles.
Alexander's invasion of India (327 BC) too falls in this period. The reader may point out why there is no mention of Alexander's invasion (or the invasion of a great Yavana king, since the Greeks were known as Yavana (Ionia)) in Mahabharata. The reason is that Alexander's invasion was not a significant event. It occurred in the fringes of ancient Indian territories. He conquered some part of Gandhara and cities like Takshasila (Taxila) but lost to the Puru king (Porus) ruling at Kuru kingdom (Hariyana) and returned after succumbing to mortal wounds that took his life as he reached Greece through sea route.