In the Attack on Titan Wikia, they often mention other nations aside from Eldia and Marley which supposedly have more advanced technology than these 2 nations.
What other known nations are there in the Attack on Titan world aside from Eldia and Marley, and why are they more advanced than Marley when only Eldia is supposed to be isolated from the world?
Aside from Marley and Eldia, the "Middle Eastern Allied Countries" (中東連合国), a certain "Eastern Country" (東の国), and a part of the world called the "Orient" (東洋) are mentioned. Mikasa is an Oriental. The Eastern Country and the Middle Eastern countries are probably part of the Orient, but these are not clear. As to whether or not they are more technologically advanced than Marley and Eldia, I don't know.
In chapter 98, the name of an Eastern Country is mentioned:
which is "Hizuru". Mikasa is a descendant of a once-powerful clan in Hizuru.
As for the technological level of Hizuru, it isn't clear if it's higher than Eldia or Marley. We only know from Chapter 107 that Paradi is about 100 years behind the rest of the world, and that Hizuru will help Paradi catch up.
In season 4 episode 4 of the anime, close to the end of the episode, they mention a woman comes from a nation of the west, a nation called Hizuru.
There's this Attack On Titan Universe map that I found somewhere in the web,
