There is no treaty or regulations on them. They are declared and then operated by air forces.This is probably off topic, but can anyone explain how ADIZ are declared/enforced? Is there any international law basis for them?
If you are a small country you have your declared sovereign airspace. (Spare me the Taiwan/China arguments for the moment I am talking in general)
If any aircraft enters that space they have to identify. If they haven’t they could be hostile or it could be some kind of issue so you launch an interception. Thing is it’s not always the case that the interceptor has the speed of climb and maneuver to rendezvous. That’s what the AIDZ is for.
It is a barrier between the states sovereign air space in international airspace where in the Airforce has the ability to better intercept and identify aircraft then decide what to do with it. Either escort or warn off. It’s only if said unidentified aircraft has crossed into the states airspace (crossing the boarder) leaving international airspace that the decision of action gains the kinetic option IE shoot down.
Of course here is the rub the sovereignty issue. Some nations don’t recognize other nations territory claims. Some nations insist they have significantly larger boarders than others recognize. It gets more confused with Taiwan.
Taiwan has an Airforce. But it is generally not recognized as a sovereign nation (save by a few countries) especially by the People’s republic of China who claims it as their territory and province with of course Taiwan stating the contrary to a point. As the ROCAF has interception capabilities it has declared an AIDZ but as the PRC claims Taiwan they don’t recognize the AIDZ as more than an nuisance. Neither side at this point wants to pull the trigger on a war yet neither is willing to yield. Stalemate. So the PLAAF will fly into the AIDZ and the ROCAF will intercept.