How did the 1919 Paris Convention establish national sovereignty over airspace?

The 1919 Paris Convention on the Regulation of Aerial Navigation was a landmark agreement that unequivocally affirmed the principle that every state possesses complete and exclusive sovereignty over the airspace above its territory, including its territorial sea.1

Prior to this convention, there was debate regarding whether airspace should be free, similar to the high seas. By establishing this principle of sovereignty, the 1919 Paris Convention effectively rejected the notion of "free" airspace and solidified the legal status of airspace as an appurtenance of the subjacent territory. This foundational rule ensures that states have the authority to regulate the entry of foreign aircraft into their territory and mandates that all persons within that territory are subject to the state's laws.1

This principle remains a cornerstone of international air law and was subsequently reaffirmed by the Chicago Convention on International Civil Aviation in 1944.1