Invasion of Demetrius I

In 186 BCE, northwestern India (parts of modern-day Afghanistan and Pakistan) was occupied by the Greco-Bactrian king Demetrius (Dharmamita), followed by the overthrow of the Mauryan dynasty by the general Pushyamitra Shunga. The Mauryans had diplomatic alliances with the Greeks, and they may have been considered as allies by the Greco-Bactrians. A key detail is mentioned by Ceylonese Buddhist monks, pointing that Brihadratha married Demetrius' daughter, Berenice (Suvarnnaksi in Pali texts).^[2] The Greco-Bactrians may also have invaded India in order to protect Greek populations in the subcontinent. He established his rule in the Kabul Valley and parts of the Punjab region. Soon, however, they had to leave for Bactria to fight a fierce battle (probably between Eucratides I and Demetrius).^[3]

The hypothesized Yavana invasion of Pataliputra is based in the Yuga Purana. The scripture describes the campaign of King Dharmamita:

47. Then, having approached Saketa, together with Panchala and the Mathuras, the Yavanas (Indo-Greeks), wicked and valiant, will reach Kusumadhvaja ("The city of the flower-standard", Pataliputra).
48. Then, once Puspapura (Pataliputra) has been reached, [and] its celebrated mud[-walls] cast down, all the realms will be in disorder, there is no doubt.
49. There will then finally be a great war, of wooden weapons, and there will be the vilest of men, dishonourable and unrighteous.

— Yuga Purana^[4][5]

Overthrow by Pushyamitra Shunga

Brihadratha Maurya the last Mauryan Emperor was killed in 185 BCE and power usurped by his general, Pushyamitra Shunga who then took over the throne and established the Shunga Empire.^[6] Bāṇabhaṭṭa's Harshacharita says that Pushyamitra, while parading the entire Mauryan army before Brihadratha on the pretext of showing him the strength of the army, crushed his master.^[7] Pushyamitra killed the former emperor in front of his military and established himself as the new ruler.