Airspace

Airspace is the air above a territory, treated in law and in war as something a state owns. Sovereignty runs from the ground up over a country's land and its territorial sea, which extends 12 nautical miles from shore. Above international waters the air is free to all, a line that produces most of the world's interception drama: a reconnaissance aircraft flying 13 miles off a coast is legal, and the fighters that come up to escort it are sending a message, not enforcing a law.

Where sovereignty ends upward is genuinely unsettled. There is no treaty altitude at which airspace becomes outer space. The informal engineering answer, the Kármán line at 100 km, has never been codified, which suited the space powers fine, since satellites overfly everyone.

The vocabulary that matters

An Air Defense Identification Zone (ADIZ) is a declared area, often far beyond sovereign airspace, in which a state demands that aircraft identify themselves. It confers no ownership. China's 2013 declaration of an ADIZ over the East China Sea, overlapping Japan's, was contentious precisely because an ADIZ is a unilateral claim of attention, not of territory. The US, Canada, Japan, South Korea, and Taiwan all maintain them.

A no-fly zone is airspace closed by force, and it is an act of war against any aircraft of the excluded party. The US and allies ran them over Iraq for a decade after 1991 and over Libya in 2011. Calls for one over Ukraine in 2022 foundered on what the term actually means: shooting down the aircraft of a nuclear power.

Air superiority and air supremacy grade how much of the sky a force controls. Superiority means you can operate where and when you need to with acceptable losses. Supremacy means the other side cannot operate at all. Most modern conflicts, Ukraine included, feature neither, with both air forces pushed back by surface-to-air missiles and the contested middle filled by drones.

Who deconflicts military and civilian traffic?

In peacetime, civil aviation authorities carve out military operating areas and restricted zones, and military flights otherwise follow civil air traffic control. In wartime the coordination problem inverts and becomes lethal. Airspace over a battlefield is layered and time-sliced among fighters, artillery arcs, helicopters, and drones by an airspace control authority, and the failures are memorable: the 2014 downing of flight MH17 over Ukraine by a surface-to-air missile happened in airspace civil regulators had not fully closed.