Before Buddhism, Hinduism was the main religion of most of SE Asia (mainland and islands). Since there really is no distinct split between Hinduism and Buddhism. The people of SE Asia just accepted the new form of Hinduism, which was later called Buddhism by Europeans. Shintoism, on the other hand was a very ancient mythology that existed before the Japanese became a civilization (by my crude standards ~300-200 BC) so there wasn't any actual spreading involved.
I'm not disagreeing with you, but i do have an arguement
What are you going to add that's not already represented that's more historically important then poland that's not in europe?
None right? I thought so.
Southeastern Asia (only 1 civ) - Siam, Dai Viet
Central Asia (no civs) - Khwarezm, Kushan
Western Africa (1 civ) - Songhai, Ghana
Northern Asia (no civs) - ?
Southern Asia (I include Iran in Western Asia, btw) (1 civ) - Split India, maybe Durranis
Southern Africa (1 civ) - ?
Pacific (no civs) - maybe Hawai'i, Maori or Polynesians
Northern America (2 civs) - split the NA
Central America + Caribbean (2 civs) - ?
Southern America (1 civ) - Moche?
Those places are in more dire need of new civs, and they're really historically important (except for maybe Songhai and Ghana). Northern Asia is even bigger than Europe (probably like quadruple the size)!
Areas that have smaller amounts than Europe, but not too under-repped:
Eastern Asia (4 civs) - Tibet, Manchuria
Western Asia (5 if you include Persia) - Parthia, Assyria, Akkad, Hittites, Seljuks, Iran? (maybe split Iran from pre-Islam Persia with Safavid, Timurid and modern Iranian leaders)
Northern Asia (2, 3 if you count Arabia) - Berbers (based mostly on the Almoravid and Almohad dynasties), maybe Numidia (weren't the Numidians Berbers?)
In contrast, Europe has 14 civs (if you include Ottomans, which I include in both Western Asia and Europe, because I base it on capitals, so Sogut is in Western Asia and Constantinople is in Europe). Do you think it's fair if we give Europe EVEN MORE? Maybe 1 more European civ. But that's it.