How about a two way invasion? Turkish people sweep into a collapsing 6th Dynasty , around 100 AD or so , while the Cheryalyan Dynasty faces incredible revolts from the Meluhans and invasions from which ever dynasty succeeds the Zhou ( Maybe a Chang Dynasty? ) in Burma and the Agripalaego. The result : After a century , a skilled Turcic King Unifies northen India , and is Meluhanized , before his heirs turning on the Cheryalyan states to the South . By 200 AD , the 7th Dynasty , a dynasty of Turkik Origins takes power in India.
In the mean time, Turks and Sarmatians ( or OTL proto Slavs) descent on Hellenized Europe and Mesopotamia and North Africa. They are eventually Hellenized too , but not before putting a Proto Slavic dynasty on The throne of the Western Empire.
The Chinese , meanwhile , also suffers massive pressure on the frontier , but holds. Between the Three Empires lie many small states formed in the Chaos . And then , the Arab Eruption begins. Within a century , Arabs boot the Sarmatian Emperors out of the West and siezes the Empire entirely ( save for Northern European Holdouts) , while also conquering vast parts of Persia and breaking into the collapsing 7th Dynasty, forming the 8th Dynasty. By 600 AD, another Chinese Dynasty falls apart. However, by 800 AD, a kind of equilibrium is re established. Four Empires reign in the world- the Chinese , an Indonesian Empire , an Indian Empire about the size of the Achaemenids , and a Western Empire of Arabic - Norman - Heleno - Roman influence.
By 900 AD, on the peripheries of these empires are several significantly large Kingdoms in Indonesia and on the Volga and Northern Europe + a Japanese Empire.