In the Attack on Titan wikia they often mention other nations aside Eldia and Marley which supposedly have more advanced technology than this 2 nations. Which other known nations are there in Attack on Titan world aside 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.
The name of an Eastern Country, "Hizuru" is mentioned in Chapter 98. 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.