Adarans are insular to the point of xenophobia, and not without reason. Of other lands Adarans know little, and they're not inclined to trust.
Riedra
Dogs led by wolves—that's how Adarans define Riedrans. Riedra is the kennel. To an Adaran, a typical Riedran is like an unswervingly loyal hound, good for working but too quick to trust the master. Most Adarans, especially those who follow the Path of Light, view common Riedrans with pity. Can the hound help that the master is wicked? Does the master's corruption make the hound evil? It is with sorrow at times that the defenders of Adar strike down Riedran soldiers, but Adar's warriors can't afford mercy. All Adarans pray for the undoing of the Inspired, no matter what that means for the common folk of Riedra.
Syrkarn
Adarans spend little thought on their neighbors to the east. The ogres, yuan-ti, and other creatures of Syrkarn rarely attempt to venture into Adar, and those that manage to breach Adar's borders rarely last long. If it weren't for the Riedran fortresses on the Syrk coast near Kasshta Keep, Adarans might forget about Syrkarn altogether.
Tashana Tundra
Many Adarans don't know the tundra exists. Those who do pay it little mind; it's far away and mostly empty. Unfortunately for these Adarans, they're wrong. Potential allies live in the tundra in the form of the Akiak dwarves.
Other Nations
Adar's chief export to Khorvaire is the kalashtar. Over recent centuries, humans from Adar have also made their way to Khorvaire. Monks of Tashalatora have set up schools as far away as Breland, and many in the Five Nations fail to understand that the martial arts of the Tashalatora are actually foreign. Adar has no embassy in any nation, however. Further, Adarans who immigrated to Khorvaire long ago are largely integrated into their respective nations. Those who arrived in Khorvaire as recently as three centuries ago, however, still have their own communities within larger settlements such as Sharn. Most such communities include a large number of kalashtar. Since Adarans are quiet, clean, and industrious, most citizens of foreign nations barely notice them.