There are two exceptions to this. One is that people from anywhere else in the world are welcome to visit or immigrate to the United Republic anytime. That's what it's there for, after all. The other is that holders of Air Commonwealth passports aren't required to obtain visas for international travel, nor submit to any border control check beyond presenting said passport. Under international law, the other nations aren't allowed to stop them, search their things, even ask them where they're ultimately headed. It's an Air Nomad's sacred right to, well, nomad, and given that they're still clambering back to something like populational viability after nearly being wiped out in the Hundred Years' War, only a titanic jerkbag would advocate for any restriction or encumbrance on the practice.

Fortunately, the phrase "national security" has not yet become the passcode to governments doing whatever the hell they want in Diqiu (though both the Fire Nation and Earth Kingdom flirted with the doctrine late in the Hundred Years' War, cooler heads somehow managed to prevail by war's end).

--G.
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Benjamin D. Hutchins, Co-Founder, Editor-in-Chief, & Forum Mod
Eyrie Productions, Unlimited http://www.eyrie-productions.com/
zgryphon at that email service Google has
Ceterum censeo Carthaginem esse delendam.