At the time Skyrim takes place, Tamriel is pretty much in Chaos..

The Civil War in Skyrim, the rise of the Aldmeri Dominion, the Empire is but a shadow of its former self...


What if Akavir saw this as an opening, and decided to Invade Tamriel?

would this be a possibility? would they be successful?

It's possible, however we don't know the military strength or skills of the Avakir

They'd run back screeming.

If Akavir invaded Tamriel in 4E 201 I predict something similar to to the Second Sino-Japanese War would happen. Both Mannish and Merrish empires would temporarily coalesce to push the Akaviri out like the nationalists and communists did in China.